Jerry,
Bill is right about the Aqua Hot not freezing if the electric is on, and there is no failure in the system or power supply. However, at the temperatures you are talking about in Florida, there is a very low chance for freeze damage anyway, but it exist. So you have to make the call as to whether or not pumping in a gallon or so of "pink stuff" is worth the it for the added insurance against a failure.
Gerald