I've had this electric v. propane debate too - propane wins!
I've got a Mr. Heater and never get it off the low setting, even when it - rarely - gets into the 30's here. Still keeps it about 30 degrees above the outside temperature, plenty comfy for me to sleep in. I only heat half the bus.
I do wish there was a thermostat on the thing tho' - it was in the upper forties the other night, I turned it on when I went to bed and woke up to 82 degrees
Occasionally I've wondered what the conversion was between watts-BTU's, like how many watts from an electric heater is equal to how many BTU's from an electric heater - anybody around here know right off?