This post consists mostly of pictures, as I actually remembered to take shots of most of the major steps. Maybe this will help someone…who knows?
Neither window leaks, and for that I am grateful. I’m OK with using them now instead of the wood windows, and in fact I think they look pretty cool. They were so easy to install!
I did take the time to CAREFULLY drill holes in the plastic bottom, to allow water to drain more easily, as especially the slanted one could otherwise overflow and start draining into the interior. Several heavy rains later I can attest to it working. 😀

Cutting the test hole for the window in the loft.
I wasn’t sure where to place the loft window exactly, as originally two very large wood framed windows were going to fill the entire space. I didn’t want it to be too high so as to hit the trim on the outside, nor too low for esthetic reasons on the inside. Hence, the exploratory hole and a lot of measuring.

After measuring inside and outside for a good placement, I used my circular saw to cut out the rough opening.

View from outside. The placement is good both inside and out.
The front is so ugly and boring still….

The RO still needs to be framed. Yeah, I did it backwards.

Framing and flashing is in

Loft window installed!

Loft window viewed from the outside

Janky window trim

Aaaaand, the finished window. Please ignore what’s happening up with the white drip edge. It was fixed later.

Finished back window from outside. Metal trim is for protection from water, but I’m not sure I like how much of it shows.
So. Water intrusion is a huge bugaboo for me. Here in the Pacific Northwest, water gets into simply everything, and then causes rot, rust or mold. I do NOT want any of those in my new home! Since I have so very much unused metal flashing, I decided to try to utilize it to keep water on the outside. The way I installed it, water goes from the roof, down the outside of the flashing, into the window flashing that sticks out, and then out the sides. Since neither window (nor the door, which I did the same way) leaks, I guess it worked.
The only thing is, there is so much metal above the rear window! I’m considering cutting some of the left-over T1-11, painting it to match the body, and cover a good portion of the upper metal. I don’t know…anyone have any ideas I can consider? I don’t want it to be too different from how I did the other window and door. Whaddayathink?