What temperature does propane stop flowing?

Since you must be plugged in at, wherever you can “camp” in Calgary in the winter, are you limited on power, or is there some other aversion to some electric heat?  Would seem to be an easier and likely cheaper short term solution since the LP furnace probably chews through the LP quickly anyways. 
Another option, have spare tanks stored inside to rotate into the mix and keep em on the full side to help with boiling a greater volume. 
or use some of your power to heat the tanks. Literally a small magnetic block heater on the tank you’re using and an old blanket around it will make the problem disappear. 
idk depends how long you need the solution for. 
good luck and stay warm!