I lived in a 36' FW for 5 years in central Oregon. Temps did get to zero several nights without any problems with water hose or dump valves.
I had a brown hard sided drinking hose (better for heat tape than the soft white hose). I taped a heat tape to this hose and covered it with foam insulation. I covered the dump valves with tin-foil and taped a heat tape over the tin-foil and covered this with pipe insulation.
I left my grey valve open and dumped the black tank when needed. The sewer hose was connected and placed on a hose support without any low spots. Worked great for me - good luck.