i've lived through 2 winters in my bus and have my tank set up with warming pads.
1 set of pads runs off of 12v. they don't consume a lot of juice. i could plug them in without worrying about the battery for a few hours. i ran my generator every evening to keep the charge up over night.
the other warmer is 110v heat tape. its wrapped around the tank so i can just plug into any 15A shore outlet and start thawing.
the down side of this set up was extreme cold, like below 0 temps. heat or not, the cold would overpower the thaw. the slug in the tank may thaw enough so that the bottom surface would melt, but then the ice chunk is no longer in contact with the heater on the bottom surface, and thawing would stop. at one point, during an extended cold snap, i had to drive south to thaw out.
if daytime temps were above freezing, the winter was easy. long periods of freezing temp would probably require boxing the tanks with their own heat.
i used a lot of ice melt, rv antifreeze inside the tank as well, just to keep things flowing.