We recently got back from our first winter camping trip. In a short time I became an expert at what will freeze and how to unfreeze it.
Our temps got down to the -5 F and with windchills to -12 to -15..
Before leaving I opened up the bottom and put pipe insulation around the fresh water line and a supplemental heat rod in the underbelly area.
Even with the furnace running(temps sometime around 50 degrees), line wrap and supplemental heat our fresh water line from the tank froze. I even had the low point pipe wrapped. I put a heater on it and unfroze it. I suspect since the line lies on the bottom and the low point goes out into the elements is the reason it froze at that point. The tank itself never froze, but I drained it and used the campgrounds water via heat tape.
I also learned that if you're going to camp you better open your gray water tanks upon arrival. If you don't they will freeze in the closed position or at least the #1 tank will, then when it fills you will have to thaw it out to drain it. Again I was opening up the bottom and sticking a heater in there. Once I got it open they stayed open for 2 weeks.
Upon leaving we realized we should have closed the #1 gray tank after some hot showers at it was stuck in the open position and temps were about 10 degrees. Not a big deal and once we go on the road and into warmer areas it closed easily.
The other problem area is the Connection bay. The bypass valve on the bottom tends to freeze up. Again a few minutes with the space heater open it up. I had a light 40w bulb in the bay burning 24/7 and it didn't prevent it from freeze.
When I travel and I know it's going to be freezing all day, I turn on the water heat and leave it on until we hit the road. It will stay hot most of the day. I drove from 10 degrees to 30 degrees on a 11 hour drive and the water was still warm.
I do keep the furnace on while driving at around 50 degrees.