I depends what you have- many RVs use a suburban brand furnace.
which is controlled by a thermostat similar to what you would see in a house- a sliding needle or dial type
the outside will have 2 vents, one for air in, and exhaust out- make sure these are clear of bug nests etc ( screen covers are sold).
so with propane on at the tank ( and gas in the tank) the thermostat should turn on the furnace for you- if it doesn;t an RV specialised repair shop should be your next call.
you'd know if it's on- noisy as heck.
driving with propane on? heres one RV'ers experience:
Mike