The Gap Decaders’ Forever Truck: Designing a Victron Overland Truck Power System for Life Anywhere in the World

Case Study: System design, specification and supply by Energy Monkey | Installed by AutoElec Wiltshire

When an overland truck is also somebody’s full-time home, office and route to the next continent, its electrical system has to do far more than keep a few lights on. It needs to provide dependable off-grid power day after day, cope with demanding appliances, recharge from multiple sources and continue working as the vehicle moves through different countries, climates and electrical standards.

That was the brief behind The Gap Decaders’ “Forever Truck”. Energy Monkey was chosen to design, specify and supply the Victron overland truck power system for Phil and Izzy’s MAN-based expedition vehicle, but our relationship with them started almost five years before the new truck was built.

For customers planning their own expedition vehicle, this project is a good example of how we approach bespoke Victron system design: start with the people, the vehicle and the journey, then specify the equipment around the way the system actually needs to work.

A Relationship That Started Long Before the Forever Truck

Paul Collins from Energy Monkey first met Phil and Izzy around five years before the Forever Truck project at the Adventure Overland Show in Stratford-upon-Avon. Energy Monkey was exhibiting Victron Energy equipment and Phil and Izzy came to the stand because they were having problems with the Victron system in their existing truck.

Energy Monkey had not supplied that original system, but that did not matter. Paul spent time talking through the issues and offered to help further, even offering to meet them after the show to look at the system.

Phil and Izzy later told Paul that they remembered that willingness to help. When the time came to specify the electrical system for the truck they intended to live and travel in long-term, Energy Monkey was the first company they called.

Their own independent 18-month review tells the story from their side and explains why they chose us. Read The Gap Decaders’ Energy Monkey review.

Designing an Expedition Truck Electrical System Around a Lifestyle

The biggest design challenge was not simply calculating how many batteries or solar panels would fit. It was understanding exactly how Phil and Izzy wanted to live and where the truck might take them.

For a serious expedition truck power system, we want to know the expected daily loads, the maximum simultaneous loads, how long the owners want to remain off-grid, the available roof area for solar, how the vehicle can charge while driving, whether generator backup is required, the temperatures the equipment may experience and which countries the truck could eventually visit.

“The biggest challenge wasn’t giving Phil and Izzy what they asked for. It was making sure I completely understood how they wanted to live and where the truck was going to take them. With an overland truck like this, you can’t design the system only around how somebody might use it in the UK. You need to think about the journey, the climate and how the owners actually want to live.”

Paul Collins, Energy Monkey

That approach is important because an overland vehicle electrical system is difficult and expensive to change once the truck is finished. Future requirements need to be considered at the design stage, not after the cabinetry, wiring and external connections are complete.

Why a 24V Overland Truck Electrical System?

The MAN truck uses a 24V vehicle electrical system and 24V engine-start battery arrangement, so 24V was the natural foundation for the habitation system. For an expedition vehicle with substantial inverter loads, 24V also keeps DC currents significantly lower than an equivalent 12V system, helping with cable sizing, voltage drop and distribution.

The electrical loads were then assessed around the way Phil and Izzy planned to live. Their truck needed to support high-demand equipment including induction cooking, Starlink, laptops and devices, television, a washing machine, habitation air conditioning and the normal 230V and DC services required for full-time life on the road.

The Heart of the System: Victron Quattro 24/5000

At the centre of the system is a Victron Quattro 24/5000 inverter/charger. The 5000VA unit was selected around the expected peak loads, with approximately 4kW continuous inverter output available under its rated conditions.

The Quattro was not chosen simply for inverter capacity. Its two independent AC inputs became a key part of making the truck genuinely suitable for international travel.

The Question That Changed the Design: “What Happens If You Go to America?”

During the design conversation, Paul asked Phil and Izzy whether they might ever take the truck to North America or another region where 120V shore power is common. It was not something they had originally considered, but for a vehicle intended to be their Forever Truck, the answer was yes.

That meant a conventional UK/European 230V hookup alone was not enough. Energy Monkey designed the truck with two external AC supply routes so it could accept either 230V or 120V shore power.

230V on AC Input 1

The normal UK and European 230V external hookup feeds AC Input 1 of the Quattro. This is the preferred supply whenever a suitable 230V source is available.

120V on AC Input 2

A second external inlet is provided for 120V supplies. The 120V input passes through a Victron Autotransformer, which steps the voltage up for the truck’s 230V system before feeding the Quattro’s second AC input.

The Quattro can therefore prioritise the normal 230V connection when available and use the alternative input arrangement when required. The same concept also gives the truck flexibility to accept an appropriate 120V or 230V generator through the corresponding inlet if Phil and Izzy ever need one.

Energy Monkey also stocks Victron stainless shore-power inlets and can incorporate shore power, generator and international AC requirements into a complete expedition vehicle electrical design.

More Than 2kWp of Solar for Genuine Off-Grid Travel

The roof carries five 405W solar panels, providing 2,025Wp (2.025kWp) of solar capacity. A Victron SmartSolar MPPT manages the array and converts the available solar energy into controlled battery charging.

For a full-time off-grid truck, solar sizing is not just about fitting the largest possible number of panels. The design needs to consider likely daily energy use, seasonal solar yield, panel orientation, shading, battery capacity, alternator charging and the climates in which the vehicle will spend time.

The Gap Decaders’ later review provides the best real-world validation: after 18 months living with the system, they reported that they had never needed to connect to mains hookup.

A 24V Lithium Battery Bank Built for High-Demand Living

The battery bank consists of three Victron 25.6V 200Ah lithium batteries. Together this provides 600Ah at 25.6V, or approximately 15.36kWh of nominal stored energy.

That capacity was selected as part of the complete energy system rather than in isolation. Battery storage, inverter output, solar generation and charging while driving all need to work together if an expedition truck is expected to run demanding household-style appliances without the owners constantly rationing electricity.

Charging While Driving

The truck can also charge the habitation battery bank from the vehicle while the engine is running. A Victron 100A Buck-Boost DC/DC converter manages alternator-derived charging into the lithium system.

For an overland truck covering long distances, combining solar generation with engine charging provides useful resilience. Energy can be replenished while travelling even when weather conditions are poor or the vehicle is parked where solar production is limited.

Cerbo GX, GX Touch and Remote Victron Support

A Victron Cerbo GX and GX Touch 50 provide the central monitoring and control platform for the system.

The GX system allows Phil and Izzy to see battery state of charge, power consumption, solar production, charging sources and system status. With an internet connection, the Cerbo GX can also connect to Victron Remote Management (VRM).

That remote visibility is particularly valuable on an expedition vehicle. Through Energy Monkey’s VRM remote monitoring and support, system information can be reviewed remotely, settings can be checked and many problems can be diagnosed without the truck needing to return to the UK.

Energy Monkey also provides Victron remote programming and commissioning and specialist Victron technical support for customers who need expert help with system setup and diagnostics.

Choosing an Installer We Could Trust

Energy Monkey’s role was to understand the requirements, design and specify the system, supply the equipment and support the commissioning. For the physical installation, Paul asked Richard from AutoElec Wiltshire to price the work.

That decision was not simply about finding an installer who had availability. Paul and Rich had known each other for around nine years, and their relationship also began with an overland truck.

A customer was having a system installed in an ex-military DAF around a mile from Paul’s home and called because they needed some MC4 connectors. Paul drove down to help and met Rich, who was carrying out the installation. The workmanship immediately stood out as exceptionally tidy, but Rich did not yet know how to programme the Victron system.

Paul programmed the system and asked Rich whether he wanted to learn more about Victron and potentially install systems for Energy Monkey. That chance meeting developed into a long-standing working relationship.

“There are very few installers I would give a job like this to without worrying about it. We had designed the system and Phil and Izzy were putting a huge amount of trust in Energy Monkey, so the physical installation had to reflect the standard we expected from the design. I’ve known Rich for years, I trust his workmanship and I consider him a friend. He’s a good guy and one of the best installers around.”

Paul Collins, Energy Monkey

For complex overland truck electrical installations, good equipment is only one part of the job. Cable sizing, protection, isolation, termination, physical layout, programming and commissioning all need to be right.

Two Relationships That Started With Helping

There is a nice symmetry to this project. Paul first met Phil and Izzy while helping them with a Victron system Energy Monkey had not supplied. He first met Rich while helping programme a Victron system Energy Monkey had not installed.

Years later, those two completely separate relationships came together on the Forever Truck. It is a good example of how Energy Monkey has built its overland and Victron work: knowledge first, help where we can, and long-term relationships rather than simply selling boxes.

Watch the Forever Truck Electrical System Video

The Gap Decaders documented the build on YouTube, and Paul Collins from Energy Monkey was interviewed about the electrical system, the Victron equipment selected and the thinking behind the specification.

Watch The Gap Decaders’ video featuring Energy Monkey and Paul Collins

18 Months Later: The Review We Couldn’t Write Ourselves

It is easy for a supplier to say that a system was well designed. What matters far more is how it performs after months of real-world use.

In June 2026, The Gap Decaders published an independent review after 18 months living with the Energy Monkey-specified Victron system. They described choosing Energy Monkey to specify the solar and electrical system as one of the best decisions they made during the build.

Their review explains that the system supports the realities of full-time travel: induction cooking, Starlink, laptops, television, washing machine, habitation air conditioning and the truck’s wider electrical loads. It has operated through dark winter periods with limited solar generation and hot weather when air-conditioning demand is high.

Most importantly, after 18 months they reported that they had never needed to hook up to mains electricity.

You can read their experience in full here: Energy Monkey Review: 18 Months Living with Our Victron Off-Grid System

“How’s the System?”

Paul still speaks to Phil and Izzy and regularly asks the same question: “How’s the system?” They are still pleased with it, and they have never had to call Energy Monkey with a system problem.

For an expedition truck designed to travel far from home, that is exactly the outcome we wanted.

Bespoke Overland Truck & Expedition Vehicle Power Systems

The Gap Decaders’ Forever Truck is one of a growing number of overland and expedition vehicle electrical systems Energy Monkey has been trusted to specify. Since this build, we have continued to work on increasingly large and technically demanding projects for specialist vehicle builders and private customers.

That includes our largest overland electrical system to date, designed for a bespoke expedition truck with a finished build value approaching £1 million. We will share that project separately if customer permissions allow, but it demonstrates how far bespoke overland power systems can scale when high inverter loads, advanced control and complex charging requirements are involved.

Whether the project is a self-built expedition vehicle or a high-value professional overland truck, our starting point is the same: where are you going, and how do you want to live?

What Energy Monkey Can Design Into an Overland Power System

• 12V, 24V and 48V expedition vehicle electrical systems
• Victron MultiPlus and Quattro inverter/chargers
• Lithium battery bank sizing and battery management
• Overland truck solar arrays and SmartSolar MPPT charging
• Alternator and DC-DC charging
• 230V and 120V international shore-power integration
• Generator integration and automatic source management
• AC and DC distribution, protection and isolation
• Cerbo GX, GX Touch and Victron VRM monitoring
• Remote programming, commissioning and technical support
• Parallel inverter/charger systems and advanced control
• Bespoke electrical schematics and complete system specification

Planning an Overland Truck Build?

If you are building an overland truck, expedition truck, expedition motorhome, 4×4 camper or high-demand off-grid vehicle, speak to Energy Monkey before deciding what electrical equipment you need.

Our Victron system design service starts by understanding the vehicle, the loads, charging sources, travel plans and the way you want to live. We can then specify and supply the inverter/charger, lithium batteries, solar charging, alternator charging, monitoring, protection, cabling and control equipment required for a complete system.

Don’t start by asking how many batteries you need. Start by telling us where you’re going and how you want to live.

Talk to Energy Monkey about your overland or expedition vehicle power system