what i do is pull the low pt pluggs and drain the system. then i put a newspaper over the air in and out on the hw heater and close the outside access door over it. this keeps cold air from circulating thru the hw heater and freezing the water.
i put a tag on the propane bottles reminding me to remove the paper from hw air in and out. then i tie a tag to the removed low spot pluggs, which i put in my sink, reminding me to check the note on the propane tank.
this should take u thru the winter and is easy to undo if u decide to take that long anticipated ice fishing trip.
my trailer stays in NE La. we probably have abt the same temps. the low here might get to 22 for abt 3 hrs abt 3 or 4 days/yr.
if u get caught with an unusually low temp, put a small heater in the trailer and set low. (open the cabinet door to lavatory and sink), if u have water lines in the cargo area...like my 5th wheel, put a 60 watt conventional light bulb in there (keep it away from paper or other flamables) just to keep it above freezing.