I have camped in my faith wheel in freezing temps as a matter of fact we picked the trailer up in the snow and then spent the next four days in Grants Pass Oregon where it did not get above 17 degrees never had a problem with the hot water heater just ran it off the onboard water tank because if water was not running the hose would freeze. Question are you using the trailer or is it in a stored condition? My feeling is as long as it gets above freezing during the day for a few hours there is not much to worry about. If it is stored small precautions go a long way.
Neil & Karol 2015 Seneca HJ