I just took my trailer down a rough logging road at 30K and the vent popped right out. Screws and all. It was too easy.
I am glad I stopped when I did because it was sticking 2" out the side of the trailer. I have had to use long screws to get through the foam insulation and into the hardboard on the other side of the wall. I am thinking I may change the screws to 2" bolts with washers and locks on the inside.
I noticed when the I pulled the chimney all the way out, I could quite clearly see the inside of the trailer albeit on the backside of the cabinet. There must be some way to get to it from inside the trailer. Maybe you could bang on the chimney to loosen any rust. I didn't measure the chimney but it must be 10" long. There is a sheet metal chimney housing with the actual 1" chimney pipe inside. The only thing you can access is the housing until you have the vent removed, unless you can pull the furnace
itself inside the unit to expose the chimney but then you're dealing with propane
lines and wires.
I hope this helps