There are several switches and the circuit board in the furnace. One or all of them could have gotten wet. Generally the switches will be okay when dry - the circuit board is a maybe. I am not familiar with your trailer but you do not have to remove the outer exhaust to remove the furnace if the furnace will come out toward the inside. The circuit board is on the "exhaust" end of the furnace.
I think I would try and remove the furnace and make sure everything is dry and try it again (or wait a few days until you think it is dry). The circuit board is easy to replace once you can get to it.
If the fan runs that is somewhat of a good sign - the fan motor time delay and the fan motor is okay. When the fan runs the air it creates actuates a "sail" switch which lets the circuit know the fan is running and it is okay to light the furnace. Could be the sail or sail switch is not working.
Unfortunately you have to have the heater removed to check this stuff. The heater can be run on the bench if you have a 12VDC source and propane.
Here is alink for the manual on you r furnace - http://rv52.com/wp-content/uploads/2...n-Furnaces.pdf