Winter RV camping

This thread has provided a lot of great information. But I have a simple question, I think. We are spending our first winter living full-time in a 1998 Monaco Windsor, and like everyone we are being hit with unseasonable low temperatures, which we weren't quite ready for. We have no trouble staying comfortable inside, and we have taken some precautions with the coach itself. We don't know at what temperature we should be more worried about the coach. We have a heated water hose. The inverter seems to warm part of the basement nicely. We are running the furnace, which takes warm air through the floor and we think it should help raise the basement temperature a little. We are expecting 26 degrees tonight and 24 later in the week. Last winter, when we were still in our house, there were a few days around 14. At what point in there should we be concerned about things freezing? At some point, should we abandon using the water systems and winterize until it warms up? Am I worrying unduly? I just need some sort of guideline. We are going to call Monaco tomorrow and see if they can offer any advice but would like some wisdom from other full-timers. Thanks!