Practice. Mode switched to electric heat will automatically revert to LP gas furnace at certain temperature BUT ALSO if the room setting is several degrees greater than actual temperature inside coach. I still forget! IF you are concerned about imitating gas heat, look at room temperature, then set desired temp just a few degrees greater. Get to that temperature, then readjust warmer.
If ambient temperature range is excessive, or atmosphere too cold for heat pump; regardless of mode setting the control panel will default to gas. When cold temperature are expected, I purge gas by lighting gas burner for several seconds to assure the furnace line will purge on limited attempt to ignite cycle.