Mostly what you need to do is refine the design so it sheds water flawlessly - just too much moisture involved too near insulation or plywood.... umnn. speaking of which, does everything pass inspection?
My 73 and 72 covers are nothing to hold out for - any nice sheet of 0.1875" or 0.250" aluminum with a piano style hinge would suit well. If you need detailed pictures of existing install I shall get some tomorrow in daylight...
The days are short and the night is long and the stars go tumbling by.. . ~Airstream~