I've hunted for a week with night temps in upper teens for at least 3 nights an 20's the rest. Daytime temps were upper 30's to 40's. Exposed black and grey tanks. Left grey dump valve open with old garden hose draining down hill. Fresh water tank has Cloroplast on bottom, top is insulated by floor insulation and has 3 inch opening in heat duct to get hot air to top of fresh water tank. Never had a problem with anything freezing. Got back home hooked up electric and dumped and rinsed black tank no problem. Did not drain fresh water tank. Kept an electric heater on low settings in the trailer and opened lower cabinet doors until next hunting trip.