Yesterday I laminated the new corner “beams”, using some marine epoxy thickened with microspheres. Since I had to let that cure, I didn’t do a lot else.
Today I removed the rear interior panel on both sides. I found there was a crack in both the existing corner pieces, and it came apart. I spliced it back in place.
Note that the side panel is gone and you can see the aluminum. The existing panels were glued and nailed in place, so I had to do some planing and chiseling and scraping to get all the glued bits off. I don’t intend to glue the new pieces in- I don’t think that’s necessary. I got the two new side panels cut but ran out of time to install them. Those will be the baltic birch ply I used on the rear interior panel.