I bought a 50' spool of 3/16" smooth nylon cord. It's just handy to have, and works well for this kind of thing.
The rubber gasket has two grooves: one each on the inside and outside. The inside groove fits on the outside edge of the glass. The outside groove fits the "pinchweld" flange around the window opening.
Install the rubber on the glass. Starting in the middle of the bottom, push the cord into the outside groove all around, leaving about 6" "tag" ends of the cord hanging out together...these are to get ahold of.
Set window in place with cord ends inside, and engage flange in groove as much as possible. Pulling the cord will spread the rubber groove over the flange. Work both ways on big windows, pushing and nudging as you go, until the last bit of cord pops out and the window is in.
For the guys at the glass shop, it takes about 3 minutes. It took me and a helper about 15 minutes, and we had to start over once.
Good luck.
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