I think you need to look at other repair shops. I took mine to a local marine fiberglass repair shop. They specialize in boats but they always seem to have almost as many RV's as boats waiting to be repaired.
I can tell you my guy would probably cut across under your window, all the way across. Order a new exterior fiberglass vacuum wall piece and fiberglass it in. Then paint to match. That is basically what he did to mine, except the cut was vertical on the fifth wheel part.
Here is a pic of the 5er before it was repaired. If you look close you can see a vertical line running above and below the bed room window. It was like this when I bought it. It was not the right way to repair it.

And this is after the repair.

And the shop guaranteed the repair for as long as I own the trailer. Good luck, John
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