We have lots of experience with cold temps (too much) being originally from Rochester, NY. Over the years we have frozen the water hose a couple of times and once froze the stinky slinky, threw it away. I don't remember any internal freezes and the includes a week in sub 32 temps at my son's house. Burned a lot of propane and kept a work light lit in the utility bay, love those inefficient light bulbs.
The temps you are talking about should cause no problem. The contents of the grey and black tanks contain many dissolved materials which lower the freeze temp and the Fresh Water tank, if kept full, will take an awful long time to freeze at the temps you are talking about. The coach we had the most winter time in was an '04 Southwind 36E 8 years of love and use.