Turn furnace on and put a heat source (light bulb, and not the LED ones, lol) in the plumbing bay.
My troubles with being in very cold usually center around non plumbing items. For example, the bay TV was damaged while camping in sub-zero temperature (TVs do not do well when exposed to cold -- especially if not used and just laying there). I would not have thought of keeping that bay compartment warm and did not see the damage until months later when I wanted to use the TV.
The salt from the roads is terrible too if you run into that.. even getting the rig washed multiple times, the surface rust looks terrible.
Do not drive in the salt is my biggest suggestion