Frozen water pipe

You may want to check the heater duct work for kinks and bends. Also have a look at the return air flow. Does the hot air travel all the way across the bay? In my case Fleetwood did install heat in both wet bays but the return air flow was screwed up and didn't travel across the whole length of the bay. I had to do some redesigning to get it right. Now the wet bays stay about 5 degrees below the living quarters.
I travel with the furnace off. The negative pressure in the wet bays, when traveling, draws heat from the dash heater into the bays.

Richard