Acdii, You’ve received much good and accurate advice, but I’ll throw this out there as well. Though it won’t help you out right now!!!You will likely experience these conditions (or colder) if you continue to rv. If you plan on keeping the rv for a few years ( to justify the work), here’s something to consider. “Dropping” the underbelly will be required. Put electric heat trace (110 volt) and foam tube insulate the water lines down to and including the valves, also tank drain lines and valves. Run the wiring to a “convenient “ location for a switch or an electrical outlet. While your there, you could put “heat pads” (12 volt) on the tank bottoms. This could provide you with much “piece of mind” in your life as an rv’er. It’s a bit of labor....you just have to convince yourself that “it’s a labor of love”! ;)