If they just won't fit and you have to add metal think of the place that will be least affected by the elements.
Also, kind of hard to explain, but try and compress it on the bottom and the brace, zip screw it in and see if you can pull to the other side of the opening.
Also, kind of hard to explain, but try and compress it on the bottom and the brace, zip screw it in and see if you can pull to the other side of the opening.