We transit the US from Canada a bit earlier, November not December. If the daytime temps are above freezing and the night time temps are below, we de-winterize and run off the fresh water tank instead of hooking up the hose. I've put a thermometer in the basement to check for temps when outside temps are around freezing just in case. Running the furnace overnight will keep stuff from freezing, don't use electric heaters exclusively as no heat gets to where the water pipes are.
If your water pipes are enclosed in the underbelly and there is some insulation there it shouldn't be a problem, running the HW heater will keep it warm.
