Vivaro/trafic/primastar.
I bought a normal LWB van and did my own conversion. I prefer the flexibility of one big space rather than the “Crew Cab” style. I have 3 Q/R rear seats but even with those in it is still long enough to put bikes in without removing wheels (although for more than 4 bikes it can be easier to do so).
It is also long enough that I can put a campbed in the back.
If you are planning to sleep in it then you will need to insulate. This will also cut the wind noise while driving.
I get just over 40mpg and I find it easy and relaxing to drive.
Get a post 2007 model to avoid gearbox issues.