I would leave my LPG heater on the lowest setting when towing my Weekend Warrior through freezing weather. I had insulated tanks, but did have the holding tank valve freeze up once. Luckily my DW had her hair dryer and I was able to thaw the valve by running the generator and an extension cord from the outside outlet. The supply line to the water heater was the most likely to freeze due to the wind chill in the forward compartment, but I ran foam insulation over almost all the forward water lines and eventually in the kitchen where the pump was located.
My Arctic Fox has all the lines wrapped in foam from the factory, so it saved me some work. Unless it's bellow 20 degrees, I don't bother to run the heat in the AF while traveling.