There are brands of real offroad vans that are nowhere near 3.5 tonne nor the size you suggest. yes they are still expensive but not much different from what KK or Quantium make.
Trakmaster, Kedron & others all make smaller vans to suit peoples preference & some under 1.5 tonne.
Im not sure why people keep up this mis-belief that ALL off-road caravans are MASSIVE HEAVY expensive things.
you are mistaken Kedron ONLY make dual axle vans- I asked 2 years ago and have recently double checked- the van in the Fraser coast odesey is not available.
They now do make a 2.5 tonne dual axle van for the mid sized vehicle mob same as the bush trackers- BUT very limited accessories and styles due to fitting in with the weight.
I have priced up the bush trackers and they can make you anything- in dual axle, can be made around 2.5 tonne for a 17 foot- but you comprimise too much.
The others like the smaller trackmaster gibson etc are caravans and are too small inside.
I'd like a "hybrid" inside sleeping, small living area if bad elements - outside living and eating when its good.
Gemhunter or spinifex will custom make a van- and this is probably the way I will go. utilising a expanding bed in the front, and including a toilet shower and bunks.
BUT the rapid will have to do the family a few years yet- plan is long service and the new camper in 2015.