Sealing heater from allowing outside air coming inside.

The exterior furnace vent should connect direct to the combustion manifold and not let any cold air or combustion gasses into the RV. Otherwise RVs are not exactly sealed that tight.

I installed a pump to circulate warm water to prevent frozen pipes. www.ultraheat.com for the tanks. Heat tape and insulation for exposed drain pipes. I also use a 1200 watt radiator style heater to supplement the furnace in winter.