Another freezing water line question

My 30 foot Class C does not have a winter package of any kind. No insulated or heated holding tanks, or thermal windows. No closed underbelly. Vinyl floors. There is no outside shower, and all of the plumbing is inside the coach. In the below picture (at my brother's house) the big door that is next to the red marker light is a pass-through that runs right under the bed. Between the pass-through and the rear wall is the fresh water tank (also under the bed). The little door, above and to the right of the pass-through, is the water fill/shore water. Below the water fill is the water pump.



I've been doing this for 6 winters now, on the Olympic Peninsula, with no problems with freezing water lines.