I've been in temperatures that reach -5 F regularly overnight for about 3 months now, and this 19' with extra insulation, double-pane windows, and spray foam only gets condensation on the windows briefly if I'm cooking something very hot and don't have the Maxx Fan on high enough.
I keep the Maxx Fan on about the third setting with the kitchen window cracked overnight, using a combo of a DeLonghi Ceramic Heater (120V)
and the propane furnace, and have no condensation issues. My wife also researched and purchased hypervent marine material
for underneath the mattress and seating cushions, and we actually stopped in Marysville, WA on the way back from Canada to pick it up - to keep mold off of the wood.
We don't have the heating pads, but I would absolutely recommend the extra insulation and window package. The only issue is the gray valve freezing, but a couple minutes with a heat gun fixes that.