Greetings & Welcome!
If it’s the same as it is here in the USA, if it’s a DIY camper van, it has to be kept a secret from the insurance company, and the likelihood of them ever paying a claim is close to zero. You just insure it as a regular van. In the case of a claim, if they discover it’s an illegitimate camper, they will deny your claim and cancel your policy.
Converted passenger vans tend to fair better with insurance companies. When I had a claim, I told them I bought it to be a camper van, and they paid, no problem. Same story with a cargo van didn’t work. Same insurance company. Passenger van was inspected by insurance company both before and after the conversion. The same was tried with the cargo van, and the insurance agent (the same one) said the company would not insure a converted cargo van unless it was done by a legitimate company, and windows had been added on both sides and the back, and it had been approved and titled as an RV by the DMV. The DMV had a …long… list of things that needed to be done both for safety, and to be re-registered as an RV. So the agent left it insured as a normal cargo van so I could at least have insurance to be legal. Got hit by a drunk driver, with no insurance, and when the claim inspector came to look at the damage, he insisted on inspecting the interior as well. Claim was denied and policy was immediately cancelled.
I should also mention that living without windows really sucks. It’s depressing and dangerous. My current 360°ree; view is heavenly in comparison. Absolutely nothing compares to lots of opening windows all the way around. Safer to drive, more comfortable camping, and you can see trouble coming before it actually arrives. Resale value is much much better too.
"Smiles are contagious, pass them on!" ~ Van_Dweller