I can't help you there, but wondered if you're removing original jalousie (louvered) windows
If you are, do take care not to damage them during the removal.
They're VERY hard to find and can be sold for as much or more than the cost of the new windows
you're putting in.
Some folks are actually replacing the sliders in newer trailers with these older windows
due to the fact that they can be open in any weather without letting rain etc. into the trailer!
Good luck with your project