Ranger Smith wrote:
I would still run the furnace as that is the only way to keep the plumbing in the basement from freezing.
This statement would be correct only if there would be absolutely no heat transfer through the floor, which of course is not true. If you heat the trailer to comfortable temperatures, you can expect significant heat transfer (some would call it loss) through the floor to whatever is there, which in your case is the holding tanks and associated plumbing. I bet you will find that the heat transfer will be enough to prevent freezing in temperatures down to the mid 20's.