It isn't just the physical weight that you need to be looking at, it is the taxable weight (taxation class) that is the main thing, some dodge 50's (a hightop van for example) can be downrated with ease to 3500kgs and classed as  PLG vehicle and some weigh far too much (4x4  or bus varient for example) to downrate.

So if you start with an empty S56 MWB 20ft long (medium wheelbase) hightop van like the red n black one at the top of the page (5600kgs taxable weight downrated to 3500kgs [b]and also for sale!!!!!![/b]) and kit it out to live in as long as the vehicles overall weight is under 3300 kgs inc full fuel and full water and gas bottle they should let you downrate it, an empty MWB hightop van weighs around 2600kgs which gives you enough to play with.

A short wheelbase S56 van empty (about 17ft long) weighs in at about 2400kgs but is much shorter and gives you far less room.

My S56 bus @ 24ft long (the circusbox one at the top of each page) weighs in at 5300kgs fitted out and loaded with circus kit and 3700kgs empty so that could never be downrated.

if you need any more help, just ask.

Then I will move this topic to the correct area and you will get a message saying it has been moved and where too (regulations and law section).