Quick update: Ended up getting the whole door, frame and all, and replaced the whole thing. The new door would have fit perfectly, but it looked really weird - bright white against a rather badly discolored frame. So, since I had it, I replaced it.
Took longer to scrape out the mountain of silicone that had been used to seal the original frame to the shell than to do anything else. The silicone was rather messily done, using way more than was required just to seal out water. I was not trying to save the frame, so I just backed out the three screws holding it on and then used the back side of a hammer to pry it off. I slightly bent the inside of the frame, but it could have been bent back and re-used, I think.
Quick job, just required a little scraping and patience.
So glad fall finally showed up so I can dive into project and camping season again
