Damaged RV plumbing is one of the most common problems that happen to extreme cold weather campers. Water expands when it freezes and causes pipes and valves to crack or burst. Here are a few tips reduce the risk.
Heat Strips - Use what's called heat strips or tape on your RV fresh water hose and cover that with foam insulation. It doesn't need much heat to keep the water above freezing. You could also spend some extra money and buy a pre-made heated water hose.
Use The Fresh Water Tank - Another option is to fill your internal fresh water tank and use it for your primary water source. Make sure the water pump is located in a warm area.
Internal Piping - Open up cupboards and access panels where plumbing pipes are located to allow heat from the rigs living area to get in there and warm the pipes.
Waste Valves - Keep waste valves closed when not using them. Wrap-up with insulation any that are exposed to the elements.
Sewer Hose - Rinse it out well and stow it when not in use to prevent damage. A more permanent ridged pipe may be a better bet if you would like to leave it connected outside 24/7.
Tanks - Only dump tanks when they are full to reduce the chance of freeze ups. Adding a little bit of RV antifreeze after dumping may be a good idea as well.