Gary:
I have the same limitation with bending heavier stock. I made mine from the heaviest sheet steel I could bend in my vise. The bends are all straight, so if you do them in the right sequence (inner bends first) you can handle pretty heavy stock with a vise and a hammer.
I did find that the flexibility of the sheet metal made it easier to install. I used #10 machine screws, washers, and lock washers. Possibly making the mounting holes oversized and using larger washers would help with installation if the material was thicker and nonflexible.
It works good for keeping brush, small branches and roots from getting into the fan. It's easy enough to make and install, that I just replace it if it gets torn up. I replaced mine this time because the dealer removed it when they did a 200 hour service (I had noticed it was dented up before they took it).
I have not noticed any over heating problems, with the shield in place, one side (toward center of tractor) is unobstructed. I have worked all day on hot days with FEL and box blade with no problems.