I have a Vauxhall Movano (2006-2010 model) long wheelbase van. It was originally a crew-bus, the chap I had if from (part of a business acquisition) had it re-registered as a motorhome. It already was lined out and had side windows, 2 extra leisure batteries with splitter to charge from engine, microwave, diesel heater, kettle, hand-washing water heater, sink, drying cupboard, fridge. Tool compartment in back, seats around a table. He made a few changes to have it re-registered as a motorhome but it was still quite "industrial."
I have done some work to make it more of a comfortable overnighter- I put in a better bed area and a £6 carpet remnant (enough to do the cabin!) adds a bit of luxury. Stage 2 will be to replace the front double seat with a single swivel, and also replace the Drivers' seat and put a removeable table between them. I do a lot of overnighting for work and use the van for staying over as hotels are getting increasingly expensive.
The Movano/Master is a good big van, the front-wheel drive versions drive really nicely and not bad on fuel. I know someone who recently picked up a former crew-bus like mine was originally for about £4k, so not megabucks. There are some downsides to the crew-bus approach- they are lined but not insulated and the seperate rear compartment makes it harder to put a loo in. However it works for me as I put my work kit in the back compartment where it is seperate from the clean office/sleeping cabin.
If I were starting from scratch, I'd get a LWB Movano/Master or maybe a VW Crafter, there's also the Peugeot Boxter/Citroen to consider although there are fewer of them about. They seem to be the tidy big FWD vans; Honest John Vans site is a useful place to get some info on pros/cons. I wouldn't get a Sprinter as (a) looking at the ones I see hurtling past me on the M-way they seem to rot and (b) they get hammered by couriers on stop-start trips. Nor would I get any exotica- a bog-standard van can be serviced easily.
Only thing to watch, if you get a big van you need to know where to take it for servicing/MOT. Not all garages have a lift that will take 2.5 tonnes of Big Van- most standard car lifts are 2 tonnes. I had a local recommendation from a neighbour who is a motorbike mechanic now, but used to do recovery work and always had big vans himself.
I have to admit, I don't get the VW thing. It seems a lot of money for a badge, OK the Crafter is a decent enough van but not intrinsically better than the Master/Movano (same van different badge) or equivalent. But whatever floats a person's boat. I think the thing is to work out what you want from a camper and then get a base vehicle that works for what you want.
GC