Dave, the tank (30 gallons) is under the floor in front of the axle. Although I have swaddled it in reflectix, the tank is not enclosed, so there is no way to heat it -- unless I build some sort of an enclosure, which is starting to sound like a good idea.
By the way, since we were boondocking, we were not worried about the black or gray tanks freezing. Those valves stayed shut till we got down out of the mountains to the dump station, and they had thawed by then.
Also, the fresh water tank itself did not freeze. I got under the tank one morning and pushed up on the plastic bottom of the tank, and the water sloshed around. We did not even hear any crackling of ice. So the freeze was very localized, right in the outflow area.
And Green, you are right that the doorway is the coldest part of the trailer, but the inside of the trailer almost never gets below freezing. Until this last week, our record low inside was 35 degrees. But this week, it was 28 degrees inside the trailer on the coldest morning. Yikes! But that is not cold enough to freeze the jerry can into a solid block.
Having said that, if I can figure out a way of heating the tank drain area without draining my battery, that would be a lot better than having to rely on my collection of jerry cans.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)
Our trips -- pix and textAbout our trailer"A journey of a thousand miles begins with a single list."