Another reason why I usually chose areas with milder winter temps! I've found on those rare occasions where the temps tended to dip below freezing at night there was never a problem. I rarely used the furnace, but opted for a small electric heater in the bedroom instead. There was never a freezing problem since the coldest temps were usually just before dawn and the holding tanks never had enough time to freeze enough to cause damage. Of course, I wasn't camping up north or in Alaska during the winter. LOL