The sad truth is .....it is totally dependent upon the design of the camper. We have spent many nights at -20 F and a few at or below a -30F. and had “no” freeze issues, with minimal things done to the unit. The heater was still cycling, though....it wasn’t off for very long periods of time! Most units cannot handle single digit F temperatures, ours had a factory warranty to a -20 F. Even “if” the unit is designed for cool temperatures, you will burn a lot of propane.
We just finished a 2 week boondocking trip, with a couple of nights below zero F.....we burned-thru about 40 to 45 gallons of propane! But....we were comfortable and the water kept flowing!
Many think that no RV can handle below zero temperatures....possibly the same folks that think the earth is flat!