Every self-build starts with the same sentence: give me three months and it will be done. Then you count the weekends. Twelve weekends is twenty four working days, barely five full weeks, and half of them will go on things nobody photographs.
In brief
- Cut every hole in the roof and sides before insulating anything.
- A van moves and sweats. House methods belong in houses.
- Size the battery from a watt hour audit, never from a forum number.
- In France a fixed conversion needs re registering, and that is not optional.
Mistake one: budgeting in months, paying in weekends
Time estimates go wrong because people count calendar months while spending Saturdays. I have no reliable statistic to offer here, and I would be suspicious of anyone who claims one, but the arithmetic is enough on its own. Three months of weekends is around twenty four days of actual work, and a chunk of those disappear into waiting for a delivery, waiting for sealant to cure, or driving to a supplier who turns out to be closed on Mondays.
The practical fix is to decide in advance which jobs you will pay someone else to do. Cutting and bonding a window into a steel panel is the classic candidate: one afternoon for a professional, one very long weekend and a permanent knot in your stomach for the rest of us.
Mistake two: building it in the wrong order
Sequence matters more in a van than in any room of a house, because everything you fit later sits on top of something you can no longer reach. Cut the holes first. All of them.
- Exterior cutouts: windows, roof fan, skylight, any air conditioning unit, plus the cable glands. Then park it outside through the first proper downpour and go looking for drips while the metal is still bare.
- Sound deadening and insulation, once you are certain nothing leaks.
- Wiring runs and basic lighting, pulled through before the panels close the walls.
- Wall and ceiling panels.
- A bed and a heat source, which is the point at which the van becomes usable rather than a project.
Getting to step five early is not just satisfying. It is the thing that keeps a build alive through its second winter.
Mistake three: treating it like a house
Borrowed house methods are the quiet killer of van conversions. A house does not do 110 km/h on the A8 with a mistral crosswind, and it does not swing between 4°C and 35°C in the same twenty four hours. Everything in a van vibrates, and everything cold sweats.
Three habits worth unlearning. Timber battens screwed straight to the floor, which trap water where you cannot see it. Vapour barriers copied from a loft detail, which behave very differently inside a sealed steel box. And self tapping screws into the body, when threaded inserts spread the load properly and do not work loose after six months of road buzz. Before drilling into any rib or floor section, look underneath: brake lines, fuel lines and wiring looms all live in places you would not expect.
One thing genuinely borrowed from housing does belong here. If you fit any combustion appliance, gas or diesel, a heater or a hob, you want a carbon monoxide alarm designed for the job. EN 50291-2 is the European standard covering CO detectors for permanent installation in recreational vehicles and similar spaces, as opposed to the domestic EN 50291-1 units sold in supermarkets. It costs less than a decent drill bit set.
Mistake four: sizing the electrics from a forum post
Round numbers travel well online and fit nobody’s van. The only sizing method that survives contact with reality is boring: list every load, in watts, multiplied by the hours you honestly expect to run it, and add it up as watt hours per day. Fridge, lights, water pump, laptop, phones, fan. That single figure drives the battery bank, the solar array and the alternator charging together.
Then apply the usable capacity correction, which is where most beginners lose half their bank without noticing. Battery makers generally advise keeping a lead acid or AGM bank above roughly 50% state of charge if you want it to last, while lithium iron phosphate is usually rated for a much deeper discharge, commonly quoted between 80% and 100%. Sources disagree on the exact usable fraction, so treat the published figures for the specific battery you buy as the authority, not a blog average. In practice a 100 Ah AGM and a 100 Ah lithium are not the same battery at all, and no amount of solar fixes that.
Charging matters as much as storage. Solar alone is generous in July on the Côte d’Azur and thin in January anywhere, so a build that can also take charge from the alternator while driving, and from a shore power hookup, is far less stressful than a bigger bank fed one way.
Mistake five: leaving the paperwork until the very end
This one is specific to where the van will be registered, and in France it is not a formality. Under article R. 321-16 of the code de la route, a vehicle that undergoes a notable transformation must go through a new approval, handled through the DREAL as a réception à titre isolé, after which the registration document is updated to the VASP category with a CARAVANE body type.
What counts as a conversion is defined at European level. Regulation (EU) 2018/858 describes a motor caravan as a vehicle with living accommodation containing at minimum seats and a table, sleeping accommodation which may convert from the seats, cooking facilities and storage, all rigidly fixed to the living compartment, with the table allowed to be removable. Read that list again while you sketch your layout, because it decides which side of the paperwork you land on.
Two more numbers belong in the same conversation. A category B licence in France covers a vehicle up to 3.5 tonnes gross weight, and a finished conversion is heavier than the same van on the forecourt. Weigh the base vehicle before you start, keep a running tally of what you add, and design your storage so the mass sits low and between the axles rather than up in the roof lockers.
Before you cut the first hole
Do I really need a full plan if I am building in stages? Especially then. Staged builds are where undocumented decisions collide, six months apart, usually over a cable route.
What is the one purchase people regret? The cheap mattress. A bed platform is easy to rebuild, sleep is not: for the same reason I fussed over density rather than thickness when I picked the foam for an upholstered headboard at home, and the logic carries straight into a van bunk.
Plan on paper, cut once, and accept that the build will take longer than you told everyone. It always does, and the ones that get finished are the ones that were comfortable to sleep in long before they were finished.
More small space thinking
Storage that reconfigures itself is a van problem long before it is a flat problem.
Updated 17 August 2026. Sources consulted: Regulation (EU) 2018/858, Annex I, for the definition of a motor caravan; article R. 321-16 of the French code de la route and DREAL guidance on réception à titre isolé for transformed vehicles; French rules on category B licence weight limits; standard EN 50291-2 on carbon monoxide detection apparatus for recreational vehicles; battery manufacturers’ published depth of discharge guidance, which varies between sources. Practical information only, not a substitute for a qualified installer on gas, electrical or structural work.
