This is a good way to do it if you do not weld or have access to one. Here's how it looked before closing it up. I had P hat type studs in my CTC so I did it very similar except there is an edge on each side to screw into so no L brackets needed.
If you have a welder and have the skills to use it, you just would use 1 inch steel tube to weld in frame as needed.
This is what it looked like framed in: I am sure you can do this for your second window.
![Image](https://uploads.tapatalk-cdn.com/20190820/ab8880457e45fda4babf09bf5ff999ec.jpg)
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