We have been using our enclosed trailers to haul our camp and then sleep in them for 15 years or more, BIL has a 26' with a forced air furnace from an RV in his, easily sleeps 4, very comfortable and constant temp as the furnace has a thermostat.
Mine is a 22' which can also sleep 4 quit easily, I use a little buddy heater in mine, I had the ceiling sprayed with Styrofoam insulation which helps hold the heat in.
Propane of course is a damp heat but given that we run a generator all night as we also pack deep freezers we both simply have a small turbo fan that we plug in to keep the air circulating, crack the roof vents and it's very comfortable.
Now I have never hunted with mine in late season, we hunt late Sept / early October so it's not really cold at night -5 or so don't know how they would be when it's -25 or more
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