At 20 F I'd be choosing an RV that had enclosed, heated tanks and valves. The heated fresh water hose may not work as well as you hope. I operate on my fresh water tank, and fill as needed.
Also at 20 f the fridge needs to be protected from the working fluid gelling. See the thread under the full time forum called Winter.....
chrisandoctavia wrote:
We plan to live full time in the RV - but would just like to be OK in locations where the temperature dropped to say around 20 overnight
We would separately buy a heated water inlet hose