This is a facinating subject. We used to advise & prepare rigs for running the Alcan. If your decision is based on towability then I'd opt for the 5th wheel, but as far as temperature control and room utilization goes a TT will work far better. Slide outs and extendable rooms should be avoided, they will be a constant source of heat loss as well as a mechanical nuisence to you'll have to consider chasing every time you move the rig. The expansion/contraction dynamics you'll be subjecting this vehicle to are way beyond anything the coach was designed for. You state you need to be self contained but you might be able to get electrical and water with no worries for waste. that makes this tough, because your not giving us a valid starting point. My advise is KIS*. If it'll work without gizmo's, thats the best way to do it. But with todays technolgy that might be difficult. The more there is to this, the more there is to go wrong.I can tell you we used to advise for hunting group trailer set ups years back when all there was was Propane brought in for the old gravety flow radient heaters. Lp lights and straw bales set around the sides of the rigs to help trap heat. Some would even erect a 2 x 6" tarp over the top of them to kill the wind. Most would cover the exterior of the rigs with 1/2 plywood just to keep the sheet metel from conducting the cold in through the aluminum. Forced air heat was not needed or wanted, for that matter because battery power was limited at best and moving air other then convection caused chill. I admit, Now with solar power, that might've changed a bit. These rigs would get set up and remain operative literally all year long. They lugged everything, and from what I gather, they're still doing it pretty much the same way.
Spent my youth working on RV's with my Dad. I'm just coming back to them now and found my child hood was not a total waste.