Just a note. We were camped in southeast Oregon in April and the temperature went down to 19 degrees. The water pump froze. HOWEVER, when we got home and to warmer temps, it thawed out and I had no damage to the pump.
Pretty good water pump in the Sportsmobile.
We have learned a lesson in cold weather camping. We keep the cabinet door open where the water pump is located and that gives it just enough heat to keep it thawed. I was up at Stanley Idaho a few weeks ago in a snow storm and 20s and had no trouble.
Watch out for your exterior fill. It is made entirely of plastic and mine froze several times with no problems but eventually cracked. I am not the only one here who has had this problem. I have added a valve under the sink so I can shut off and drain the lines to the fill valve. If you camp in cold weather often you may want to consider this.
Our 18 gallons of fresh water is under the sink in the rear of our van in closed compartment. Has a duplex outlet under the sink and plug in a 60 watt light when it is cold outside. Keep the light on while traveling and if possible while camped. After being on for 24-48 hours it even takes the chill out of the water.
I've frozen mine and also run it for hours til it was smoking hot (fill tap was open so it cycled into fresh water tank). Thought I'd be buying a new one at least 3 times but it still seems rock solid.