Ron - a few things,
1) The wider the rear axle - the wider you need the frame to be to put the suspension close to the tires.
2) The wider the rear axle - the stronger the axle must be to absorb the torsional loading.
3) You not only need dual wheels - you must have dual wheels for stability and safety.
4) Considering the cube-van shown above. Pull the leaf-springs and retro-fit an Air-Ride suspension. I had Air-Ride in my 38' motorhome and it would drop that coach a good 10-12" closer to the ground when I was parked.
That old truck with the front-wheel drive system and trailer on the rear - man I cannot imagine the stress on that frame.. I surely hope it is made of fully boxed 4x10 steel..