In my MH they tell me the furnace ducts willl (normally) keep the water in the tanks liquid... If, that is I choose to burn up propane all winter.
However they also say if it's really cold out to open lower level cabnet doors (under sinks and the like, Remove access panels to water pump and water heater and the like to improve hot air flow in those areas.
Ok, I may do that next year, for now, I just drained all the tanks, blew out the lines with compressed air and re-filled with pink stuff (RV-Antifreeze) enough to insure that the traps are protected and that I have liquid to flush with when I hit the road.
Plan on adding real water (and bleach) at my first fuel stop,,, Just before I leave Michigan, Jan 2. (will pump anitfreeze to the holding tanks and dump) Will drain the sanitazer mix the next time I re-fuel and fill with drinking water