In reply to Tigger:
Just a thought, many of these vans are essentially the same as people carriers, eg the Peugeot Expert is the same as the Peugeot 807 without the seats or windows.
You may find the tax and insurance on the people carrier a lot less than the van and if nothing else it widens your choice of vehicle when buying.
You can make a diy boot conversion along these lines like this
http://www.amdro.co.uk/boot-jump-camper-car/boot-jump-with-screens-water-bo...
which allows you to "convert" it to a camper as and when you need it whilst retaining the rear seats for passengers when you want.
Lots of people seem to do this with smaller car/vans like the Berlingo/Partner/Kangoo etc but I find them a bit small.
Instead I recently bought a mk.2 VW Sharan for this purpose (Same as a mk.2 Ford Galaxy/Seat Alhambra). Its nice to drice, plenty of power and averages about 43mpg on a mixed use tank but closer to 50mpg on motorway/A road driving. I've taken out the 3rd row of seats so its basically an enormous 5 seat estate car for day to day use.
I suppose it depends on whether you want a permanent conversion or not.