Of all the work done so far, I am most proud of these windows. I used Stuarts built on site method. The outside glass is 3/8” laminated set with glazing tape and caulked with PVC trim cleating it into place. The interior is 5/8” glass set on a neoprene seal and cleated in place with some interior trim ( interior glass not shown in this photo.) I stuffed the 1” gap between the frames with rockwool, then I found these great 1/2” polyester felt boards and covered it all up. The felt cut amazingly on a table saw and its rigid, but not so rigid that it creates a flanking path but has a nice friction fit. I also used a brad nailer to tack it for good measure. It looks super cool too.
Also hid 40g of silica under the bottom felt. Since the inside window is just compression fit, I can always take the trim off to remove the glass and replace the silica if I have to.