So we got the windows in! The two part gasket piece worked perfectly.
After my initial cleaning I did a last minute clean of the fiberglass window hole with acetone. This worked really well, but be careful, I got a little on my emergency exit sticker and it took some of the paint
off! (Well, it is nail polish remover, what did I expect?).
Then I fit the gasket around the fiberglass window hole, pressing it into the corners. When I felt it was pressed in the corners as well as possible I cut it off, with about a centimeter extra. Then I forced this to fit - you want the two cut pieces to have pressure against each other to make a good seal.
Then the window got put in. This actually worked better than I expected, mostly due to the horror stories I had read here! The locking gasket tool was very helpful for this part of the job. It was a good shape to press the window into the gasket. You definitely need two people for this, one working on the inside and the other on the outside helping to press the rubber gasket inwards to help and making sure that the window doesn't pop out in the corners. Having the outside person push the gasket inwards with a butter knife helps too.
Once the outer gasket is in then the lock strip has to be put in place. We used very soapy water for lubrication which we applied with a turkey baster that has a very sharp end.
As you can imagine this procedure lead to some hilarity over the instructions being given. 'More lube!' 'Press it there' etc....
All joking aside it was a tight fit and did cause some back strain. (Hmmm that still sounds funny!)
The lock strip tool was amazing. Note that putting the emergency pull tab back in place means you need to start the lock strip tool on either side of it - it is held in place by the locking part of the gasket coming out through it.
Again when you get all the locking gasket in place and need to cut it make a little longer and force it into place.
Ah, all done! (for one window!)