Hi,
Chances are that the heat pump (rooftop air conditioner) will come on if it is above 40F outside, and try to warm the RV. Once below 40F outside, or if you set the thermostat more than 5F higher than the room temperature, then the gas furnace normally will take over.
Of course anytime there is no 120 volt power to the RV, it will change over to gas furnace.
Personally, I normally use a 120 volt electric heater when I am in a RV park. But most nights, I spend out dry camping, and use my Olympic Catalytic heater, that does not need any 12 volt power. However it does require a roof vent and window be open.
Fred.