Achilles Heel: Heated Tanks but not Water Lines
On my 2018 Siesta 24ST, on this winter's Southwestern trip, I discovered a significant flaw in its cold - weather water protection. On two mornings when boondocking, with overnight temperatures hitting mid or low 20's, the next morning I had no water from any hot or cold faucet. As the morning temperature rose, the water began to flow again, and there was no apparent permanent damage. The Siesta is equipped with "enclosed heated tanks", and unlike the electric pads used in other rv's, Thor achieves this by piping a small duct from the furnace through the bathroom, forward to the location of the black and grey tanks. This pumps furnace heat across the top of those tanks. (The fresh water tank is already above the floor, beneath a bunk, so protected.) While I don't know how effective hot air across the top of the tanks, when the liquid is in the bottom, will be, that is not where the problem turned out to be.
Thor runs the water line from the water pump down through the floor, to the cold outdoors, then right angled into the basement compartment which contains the metal box where the city/fill/normal selector switch is located. All water must pass out to this selector, then back in to the coach. There is no heating in this compartment or box, and the water lines to and from are completely exposed to the elements.
As for the exposed water lines, I'm planning to build up a heavy layer of spray foam around them. I'm debating whether they should be also first wrapped with heat tape. Also, the unheated selector switch / box seems like it's going to need to be addressed as well, though I haven't tried to see if the box face can be removed to get to the inside. There again, I'm debating whether to use just spray foam, or also heat tape.
Has anyone else been through this problem yet? What was your approach and results? Thanks.