My Prowler TT has an totally exposed fresh water holding tank that has a factory installed heating pad on the side next to the water demand line, an Ultraheat TH726 13.5v. I have never had this type heater on a unit before and want to find out what experience others have had regarding battery drain times with various outside temperatures. How long does it take to raise the tank water temperature say 10 deg with 30 gal water? What is the proper operation, i.e. if it is 10 deg. outside can I allow the tank to freeze some and turn on the heater each time just before I need fresh water?