You note that temps MIGHT drop below freezing "here and there". I don't think you need heat pads if it is just an occasional overnight drop where temps are back above freezing during the day. It will take a while for thanks to freeze
You can buy the heating pads. No problem there. My trailer has them and there is one switch on the control panel for them - labeled appropriately.
Hard part of the job will be fishing the wires.
Note that they only work when hooked up to shore power. Resistance heaters will kill even a huge battery bank quickly.
My trailer came equipped with the pads in the link below. I have one large pad on each tank and a small pad on each drain pipe.
FWIW, there are folks who boondock winter camp - no electricity other than, maybe, a portable generator. They use bottled water and just dump into the tank. The liquid will freeze but not cause any problems. You just have to wait until things warm up to dump the tanks.
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S.E. Mich. Flagstaff 26FKWS / 2019 F-150 3.5 EcoBoost SCrew Propride