The most common issue with an RV furnace is the sail switch. Here are simple to follow steps to help determine the cause of your RV furnace issues.
Before digging into diagnosing a furnace, first thing is to turn thermostat off for 1 minute and then back on, after approx 20 seconds does the furnace blower motor come on and then off in approx 20 seconds? Or does blower not start at all? If the blower comes on for approx 20 seconds and then stops and nothing else happens (no clicking, no sound of ignition coils, no smell of propane) that is a sign of a sail switch stuck OPEN (rest position) and is defective.
However if you the furnace make no attempt to start the blower fan motor at all, that MAY a sign of a sail switch stuck CLOSED (operation position) one way to know if it is a sail switch stuck in the closed position is to LISTEN to the control board inside the furnace, the sound you are listening for is a very low volume but high pitch sound coming from the control board when the thermostat calls for heat, if you hear that sound then the sail switch is stuck in closed position and is defective.
If neither of these are the case you will want to move onto the next phase of testing.
It is important to understand the testing procedures and use a quality multimeter like the one listed on our tools page: https://rv-service.com/parts
If at ANY time you do not feel comfortable, STOP and call a qualified certified RV technician.