Another option is the CheapHeat electric strip heat add-on to the furnace. Ours has 2 each 15,000 BTU A/Cs, the CheapHeat system added to the propane furnace, and a fireplace. Although you have the option to switch between gas and electric heat on the CheapHeat system, we've never had to use propane to heat our 5th wheel in temps down around 30 degF - just the CheapHeat system and (if desired) the fireplace will keep everything toasty down to freezing, which is just about where heat pumps will give it up. There's heating capacity to go lower as the furnace (on electric) and fireplace were still cycling at 30 degF.
Rusty