Interesting thought on the repair. Here's a few thoughts I had after reading your post.
My Jayco has a diamond plate section on the front and it is about the same thickness as the tin above it. In other words I would not go too thick on the patch piece, you're covering not bulletproofing.
You could have the patch made to fit just inside of the open area and not go under the edge trim or piece above it. You are already sealed with the original panel, this panel is just cosmetic.
But they you would have to use a lot of screws to hold the two panels together and that adds a lot of leak points.
My neighbor had to replace a panel like you describe. He just measured and had a metal shop cut a replacement panel that slid up under the panel above it and under the corner pieces. I think it took him a day to repair it.
in my opinion replacing the panel is the best way to do this.
Good luck with it whichever way you choose to go.