I removed my underbelly to add a second water tank and here is my general thoughts on the tank heaters. There is one on each of the three tanks. The heating pad for the gray water tank had come unglued and was just hanging by the wires. They draw 7 amps each so the will quickly drain your batteries if boondocking. Besides, it seems to me that the small water line coming out of the tank would freeze long before the 40 gallons of water inside the tank would. Without A/C power to run a small space heater underneath I don't believe there is really any good way to keep things from freezing except in the very short term.
Seasonally in the Grand Marias, MN campground
On the beautiful shores of Lake Superior
2012 Ram 2500HD CTD