I would look for a short possibly caused by a rodent chewing the wires. You will need to remove the furnace from the TT to see what is going on. Not too bad once you have done it. You can run the furnace with it removed just shut off the propane. They generally will try to start and the blower comes on then it will shut down if it does not light by the 2nd or 3rd attempt. At any rate you have enough time to figure out what is going on. If it shuts off within a couple of seconds look for a short. If it seems to try to run then fuse blows look for what is keeping the fan from turning. Make sure the casing is sealed when you put it back together there can be some air leaks around the flimsy assy. Some duct tape to seal any air escape.