Fred,
The basement heat in your coach is supplied by the Aqua Hot, so if the basement heater is working, the Aqua Hot unit is operating and therefore it can not freeze. In Keith's case the electric water heater is the Aqua Hot unit, so if it is operating, the Aqua Hot unit is hot. The problem arises when someone just uses an electric space heater in one basement bay with the Aqua Hot turned off or malfunctioning. In this scenario the Aqua Hot and the water bay are not protected in cold weather because the space heater can not circulate heat to these areas like the built-in basement heater that operates with the Aqua Hot unit. So in really cold weather, Keith's space heater back-up plan in the case of electrical power loss or if the Aqua Hot unit malfunctions, it may not work, and we have all seen both things happen at sometime. Therefore, with a coach that is stored in really cold weather I always recommend that it be properly winterized with RV antifreeze only (the pink stuff).
Gerald