Thats a pretty nice testament to the weatherability of your AF TC. With some of those temps it would be difficult to keep any RV from freezing up. Im glad to hear that you wired in a switch to operate your basement fan while running electric heat off of shore power. I did the same thing. If I was going to be in those kind of temps and hooked up to shore power, I might consider placing a small heater in the hallway just away from the basement vent/fan. That way you would get more of a blast of direct heat going into the basement. I installed 1000 watt electric baseboard heater (make is Dimplex) so I would use that plus the portable heater for the basement heat.