We have stayed in below zero temps and we just put a thermostatically controlled INCANDESCENT 100 watt trouble light in the wet compartment. The trouble light is what was used in garages and provides a place to install a bulb that has a wire cage around it for protection. This 100 watt bulb provides enough heat to keep all of the water lines, our water pump, and our drain connection from freezing. We usually keep the fresh water tank topped off and only hook up once a week or so to empty the waste tanks. Since the water hose is only hooked up to top off our fresh water tank, we don't have to be concerned about it freezing.
Thermostat outlet plug for light
