Most insurance companies will either insure a camper van, which must be registered as such, and have windows etc, or they will insure a panel van, without insuring the contents.
UK
www.cis.co.uk offer free Europe cover as part of the policy. My stealth camper was only insured as a panel van, but I took the risk and didn’t have any problems.
You can try www.adrianflux.co.uk who are specialist insurers, and I know other people have used them for insuring custom campers.
