As stated, a lot depends on the temperaturea and weather and the internal temperature preferences.
We've seen $100+ monthly charges in December and January heer in southern California. It may also be a benifit to do a calculation of the costs of electric vs propane heating to minimize your costs.
I haven't looked at heat pumps but here the electricity cost is $0.22/KWH and propane is $2.68 per gallon, running propane heat is cheaper than either a small electric heater or a heat strip on your A/C unit.
You can get the stats on-line for BTU's/per gallon of propane and compare them to BTU's/KWH of electricity (making some efficiency assumptions) then do the comparison based on the pricing at your RV park
