Not all companies offer campervan insurance, but you can always ask your current provider. I would look through a comparison site (there are several for motorhomes / campers) or a broker such as C&MC or Adrian Flux. Camper policies usually include camping gear, personal belongings, continental cover etc..
Now, be careful as you mention your car. Many companies will only give you NCD on one vehicle (another rip off), so look for one who will either give your full NCD on both or at least a hefty introductory bonus.
We avoid any problems by having the car in my wife's name with me as a named driver, and the camper in my name with my wife as a named driver.
------------- Two drifters off to see the world.
I'm tired of reality, so I'm off to look for a good fantasy.
When I bought our first MH, about 8 years ago, Saga were happy to give me the same maximum NCD as I had on my car, and until this years renewal I had always found their rates very good indeed. I always shop around every year and generally could not get near their price but, as many companies do with existing customers, they upped the cost this year more than I thought was reasonable and so I moved to Comfort, who specialise in MH`s.
I am sure that when I come to renew at the end of the year and get a quote from Saga as a new customer they will be competitive again.
I bought my camper in January. NCD is used on my car of course. Principle Insurance gave me 5 years NCD as a starter offer. I have no connection to that company.
I don't know what size of van your thinking of purchasing but if your looking at something like a VW or similar so you can use it as a second vehicle you have to keep in mind the you will need "social/domestic and pleasure inc traveling to and from place of work" which can be more difficult to find.