Great! Congratulations with your work and thanks for the writeup.
As our Boxsters are coming out of storage many need a new window. Replacing the whole top because of a cracked or ripped window is not only expensive but also kind of wasteful, with proper care the top can probably outlast the car.
I have to replace my window too and I'm planning to do it myself, so I have a couple of questions. My top seems to have had its window replaced by the previous owner already, but they did a particular bad job. The original window is stitched in between the canvas. In my top someone just cut out the original window, left the edge in between the canvas and stitched the new window to the inside of the canvas. Of course this really sucks because the sharp stitches are on the vinyl surface and will start cutting into the vinyl. I opened the top when it was pretty cold still (well above freezing, though) and the stress just pulled the stitches through the vinyl where the vinyl folds.
So, first question; did you stitch the window in between the canvas, just on top or did you put something over the vinyl to prevent the stitches from pulling through?
I know that your window is DOT approved, but 40 gauge sounds awfully thick. The usual stuff for campers, etc. is 16 gauge. Being this thick does your window fold easily?
What kind of stitch did you use? I think that for jobs like this a saddle stitch is appropriate. It works with 2 needles at a time and you use an awl to pre-poke the holes. The advantage of the saddle stitch is that the window is kept in place by 2 threads, so even when 1 thread breaks the other will keep the window in place.
Oh, dear this starts sounding like a quilting forum....
Forgot; where did you get your thread?