We have a National Tradewinds and to my knowledge, the bays are not heated. Sooooo we put a heater in one bay with a fan to circulate the hot air throughout the bays. I plug the heater and fan into a separate 110 source and run the cord to the RV. My bays are normally 4-5 degrees warmer than the actual outside temp and this procedure seems to work quite well.
We use an electric controlled heater in our bus which we set at 65 degrees. So far that arrangement has worked for us and we have seen temps down to 20. We have not had any issues with frozen pipes. I can't say what might happen in colder weather but we can always turn on the LP heater of which we have 2 to warm up the house more which I think might help warm up the basement. Like everyone else has said the spray insulation is not the best solution for keeping pipes warm.