Interesting evening spent diagnosing heater blowing fuses

So I figured I'd run the heater in the TT since its been awhile since we used it. Turned it on. It tried to run and blew a fuse. I checked electric connections for corrosion and tried and again blown fuse. Put another fuse in checked that unit was getting power with volt meter and it was. So I proceeded to remove entire heater from camper. Wasnt too bad to get out. I had a feeling something was a miss in the blower. Took the housing apart and it was packed with mud dauber nests. Cleaned out everything or so I thought. Put it all back together and unit ran great except what sounded like a rubbing sound on the blower fan. Ended up taking it apart two more times before I found that last piece that was very hard to see and was rubbing the fan just enough to make an irritating rubbing sound. Will be putting duct tape over outside vent while it not in use.