If the furnace will not light, there are a couple of possible reasons.
First, the board could be bad. You can take the board into an RV dealership to be tested.
Second, it could be low voltage. Make sure you have ~12V getting to the furnace.
It could also be the thermal relay that allows the blower to run for up to 90 seconds before the burner ignites. However, on your furnace, this relay is probably right on the control board, with older ones it was external to the board.
It is also possible, but less likely, that the high temperature limit switch is bad.
Finally, it could be a bad sail switch. The sail switch sits in front of the blower and closes once there is sufficient airflow to support safe combustion. If the sail switch is stuck, damaged, or not getting enough flow, the burner will not light.
Oh yes, and it could be the squirrel cage fan is loose on the motor shaft, preventing the sail switch from getting enough airflow.
This is all assuming that you have proper propane getting to the burner and that the furnace is not TRYING to ignite, and can't due to lack of propane.
All of these you can troubleshoot yourself, but some you will have to remove the furnace to track down. I would measure the voltage first, followed by having the board tested. HERE is a manual for your furnace to help you troubleshoot. Let me know if I can assist you further.