The heater in any rv would run constantly and probably still not keep up. I'm with west end on the cargo trailer. You need thick insulation all the way around and then go with a roof vent to crack open and one or two good windows so you can let air in. Use a porta potty and take it with you to dump. Water, food, cooking etc can all be worked out. It would be a job but it all depends on the pay off. Go on youtube and look for rv's in the winter up in that area.
  My furnace would probably run constantly at 30 degrees or maybe a little higher. When we first got it we were still in the 40's and the furnace was on and off, over and over. We looked at each other and I said what the heck would you do if it was actually cold out!