Forgot to mention that there are a couple of screws on the outer door frame that you'll have to remove (they/it should be very obvious).

For the four flush rivets to secure the rubber to the vent frame, I picked up a pack of copper rivets from the hardware store. I then used a dull pincer-type nail puller to crush the long end of the rivet down. This succeeded in splitting the long part of the rivet, but I was able to easily smash it flat using a drift and a hammer (carefully). This was the hardest part.