We've used our truck camper alot in the winter, including a winter trip up the Alcan. My wife wants full function(hot showers, etc). When we are traveling to or actually camping I'll just run the cabin heater and h20 heater. Done that down to -33f(heaters running nearly non-stop). The pain with our style is when we transition back home and the camper is stored outside. We have to drain and flush everything.
-Chris