I amazed that the likes of Admiral or even LV are covering these.... my experience was a nightmare last month.
I could quite easily go online to a comparison site and put in my Reg, correct Vehicle shows up (California Campervan) and get loads of hits starting at £38 a month!
However, clicking through some of them decided even after quoting they couldn't/wouldn't cover it.
My current (at the time) Insurer went pretty much all the way through to cover it and failed me when I said I wasn't keeping it in the garage.
Having done a lot of research it seems that these "normal" insurers might cover you, but they won't give you the cover a proper motorhome insurer will.
I even read somewhere of refusal to pay out because despite saying they'll cover it they actually don't.
I tried Motorhome Direct (AKA Howdens) only to find out they use Victor Millwell and Devitts - however, both came back more expensive.
I ended up biting the proverbial bullet and paying double what my old Volvo was costing me and forking out £700 with Caravan and Motorhome Club ( which turns out they use Devitts but cheaper than Howdens) - first time owner I wanted the most comprehensive cover, and out of the out of the 5 or 6 I called they had it.
There's a great
Comparison Tool on their website where you can put all reputable Campervan Insurers in and see the immediate difference in cover level.