A bunch of progress since the last post.
An idea that I stole from Ed Kranz was to take some used carpet and cut out a spot for a back-riveting plate. Like him, I had to shim underneath of the plate to make sure it sat proud of the carpet surface. The carpet allowed clecos to be inserted from the inside of the structure and poke into the carpet without disrupting a solid surface to rivet against. After a few sessions of adjustments, I finally got it just right to be a solid setup. This has made very hard to reach areas to rivet with just one person much more doable.
I assembled the right side first, followed by the left side, to keep the structure as open as possible for access to back riveting. One mistake that I made was getting the bottom aft skin on top of of the J-channel stiffener when it should really be between the outer skin and the stiffener.
I had to drill out about 17 rivets to pull the bottom aft skin out and correct. In doing so, I buggered up one hole by somehow tearing the dimple.
Some other pics of the progress by the end of the weekend.