Coldest we have stayed in RV unwinterized was 19* all we did was run propane heat and a 1500watt heater. We don't have heat pads, but I think the basement vents are near or provides some warm air. The electric heater is actually used by us to overcome all the glass in the front and the fact there propane heater is physically at the rear of the coach.
Point of note, we were not expecting those temperatures, I would have winterized had I had my 1 gal Makita compressor to blow water out.
I am traveling now and fully winterized. I have my Thetford portion potti in bath room and plenty of bottled water.
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