January 14

Today we installed 2 windows. These horizontal sliders were purchased from JC Whitney, though they seem to have run out recently. Their customer service people are trying to find more via the special order process, so we'll see if we can get the remaining 6 windows we need. We have another option -- marine windows from Fuller-Brush. UPDATE: We found our remaining 6 windows at Buccaneer Manufacturing. Our radius-corner, model 5900s should arrive in 3 weeks.

After tracing the outline of the trim ring, we used a 3 1/8" hole saw to deal with the radius corners of the window cutout.
Close-up of our wall sandwich. With the benefit of hindsight...I'd rather have more insulation that that huge 3/4" piece of plywood on the outboard side.
Repeat the hole-saw trick at the other 3 corners...
...and connect the (big) dots.
After a little work with sandpaper to smooth out some funky lines, the trim ring fits nice and snug.
Apply the supplied gasket material to the inside perimeter of the window. This gasket gets mashed between the window and the exterior plywood.
The windows are set for 2 1/4" wall thickness -- ours is exactly 2 1/2", so we had to get longer srews than those supplied with the window. We also added black weatherstripping between the window and trim ring to hide the resulting gap. It also breaks the thermal bridge between the window & trim ring.
2 done in 4 hours, including 2 trips to town for parts -- installation was fairly easy.
The windows passed the "hose test" with flying colors!