Camping well below freezing - Sweden over winter

Interesting thread! I have not been in extreme cold.

I am curious about heating. Since the person has "electric" at the campsite, what about electric heat? Everyone keeps talking about propane heaters. Put an electric heater somewhere in the camper. I figure electric heaters don't put out as much BTUs as a propane forced air heater, but would they be able to keep the camper at least livable (well, survivable)?