Winsum, makes me wince some, I think I prefer something winsome.
Don't know that any mainstream manufacturer (OK perhaps Concorde, or Clou) makes a van really suitable for fulltiming, or at least one conforming to my definition of such a van. They leave that niche market to the custom builders or self builders. Nearly all build to suit weekend use with the annual 4 week holiday in mind, which probably covers 95% of their customer requirements, the main variation in any range being the number of berths, or a tweak in the layout. Italian vans often seem to be prime examples, with specs. typically comprising 6 berths, a kitchen comprising a sink bowl and a 2 burner ring all on a 3.2 tonne Fiat.
The allowable payload is the giveaway, even something like the Chieftain (MAM 4.5 tonnes?) only has 1 tonne? By the time you load a scooter, water, gas, chairs the wife, most of that's gone. So at best you're continually running at or near maximum capacity for brakes, tyres, suspension, not good in my book, and at worst possibly overweight on axle or overall.
If you're going over 3.5 tonnes then you might as well get as near as possible to 7.5 tonnes.