I assume you mean a UK style one, not a US RV that tows an SUV behind it just to do the shopping...

I've got a 2,0 diesel Transit SWB, it's reasonably manoeuvrable, not too thirsty (30mpg), slow especially up hills, high so watch car park entrances and crosswinds, comfortable enough to sleep in if you park it on the flat. It's quite cold in winter and hot in summer unless you open the windows and let the wasps in.

One thing to watch out for-- how easy is it to set the bed out? In my brother's VW, you have to turn the seats round (which involves opening the doors), and assemble a jigsaw of cushiony bits, which is not something you want to do drop taken in the dark. (by the way, it's for sale, but he wants £15000+ for it).