Mike, I had a hard time getting the vent assenblies out as well. Seems years of sitting outside rusted that bottom bolt solid to the captive nut, and even after soaking in PB-blaster it wasn't budging. I got my entire arm inside the door and could feel the bracket try to twist off as I applied torque to the bolt.
Finally, I drilled a hole in the inner doorskin and cut a tab directly over the offending bolt. With a bit of the skin peeled I could grab the bracket w/ vice grips and hold it while I torched and twisted the bolt free. Once I got it out of there, I tapped the doorskin back flat and slapped some fiberglass over the hole.
