I made a depressing discovery on Monday when I took a close look at the canopy. I noticed that the edge of the plexiglas was touching a diagonal tube on the canopy frame. This would put a lot of stress on that spot, and a crack would likely start there. Any crack would probably propagate up the canopy. Very bad news.
The instructions recognize the potential for the edge of the plexiglas to touch the canopy frame vertical and diagonal tubes. The builder is instructed to relieve the edge of the plexiglas in half-moon shaped spots to keep it from touching those tubes. I had done that, but I hadn't removed quite enough plexiglas at that spot. I had noticed this a few months ago, and marked the plexiglas where it needed to be removed. But I couldn't do the work then as the plexiglas was temporarily riveted to the frame, so I planned to do it when I removed the plexiglas later. But I forgot, and I was in too much of a rush when I riveted the assembly together on Sunday, and I didn't give it as close an inspection as I should have before I started riveting.
I couldn't leave the plexiglas touching the frame, as it would almost certainly crack. I couldn't drill out the rivets and remove the plexiglas as I had used marine adhesive to seal the skirt. I would almost certainly damage the skirt and canopy when removing it. I had to devise a way to fix it in place.
I grabbed my collection of needle files and started filing the edge of the plexiglas. It took hours, and hours and hours, but I eventually was able to file away the offending plexiglas, and then smooth the new edge very carefully. It took all week, but it turned out OK. Lesson learned (again) - Don't be in too much of a rush. A few minutes of haste can require hours to recover from.
Several RV-8 builders have noted that the rivets along the top aft part of the canopy skirt eventually move a bit, and this cracks the paint. They said that if they did it again they would put a layer of fibreglas over those rivets so any movement wouldn't crack the paint. I decided I should take advantage of their experience.
Today I masked off the lower portion of the canopy using electrical tape, and cleaned and sanded the canopy skirt. Then I cut some 1" strips of 1.5 oz "deck" cloth and fibreglassed it over the row of rivet heads at the top of the canopy skirt. Tomorrow I'll pull the peel ply off and see how it turned out. If it looks good, I'll roll a couple of coats of thinned resin over the filler on the skirt and start sanding, filling pin holes, etc.