You’re probably better off insuring your camper through a specialist broker rather than just using the same insurer you use for your car(s). You'll avoid all the "it's not a motor caravan"-type nonsense and they'll usually offer much better terms for things like European cover and Personal Effects cover.
Personally, I'd recommend Comfort Insurance if they're anywhere near competitive on price for you. They're underwritten by Aviva, they understand the campervan/motorhome market, they're easy to deal with, they provide great coverage and they offer new-for-old cover for vehicles up to 3 years old if you're the vehicle's first registered owner.
