We left home on Dec 19th with temps in the mid-to-high thirties, traveled through Ky, Tenn, Ark, Ala, to the Florida Panhandle, where the temps at night got down in the high 20s. The day-time temps were always above freezing, so our basement temps remained good with the HH going. We are paranoid about freezing up, so we didn't de-winterize until we got to Florida, but then we went through the cold they had in the north. We check basement temps constantly on the Aladdin, and have separate temp sensors in each bay going to an indoor read-out.
I have learned that as long as ambient temps are above freezing most of the day, going below freezing at night is not a problem, as long as the HH is running. It's the ambient temp being below freezing for an extended period, day and night that is the problem.