The heat pump would be lower cost. I would get it fixed or replace the unit. Generally heat pump will provide 2x the BTU per kWh vs a resistance heater.
Resistance heat vs propane is about a wash from the calculations I have seen. Propane you need to go get, electric is right there so convenience is an issue. OK to use a bit of both to say run one space heater and let the propane do the rest. May need both space heaters if the propane comes on a lot. If all is off while you are out all day the propane will re-warm the RV quicker.
