[MikeJ675]

sounds like a good idea. If I remember correctly, duct tape is still not allowed on bots.

thin lexan or another plastic may work well. You may need to heat it to get it into the proper shape, though. If you have the ability to do so, making the cover out of carbon fiber/fiberglass would be pretty nice looking(you can buy this in non-hardened sheets and use a resin or epoxy to harden it over a mold I believe)

The main thing you need to make sure happens is that there is a good seal and that the cover piece is smooth. Assuming it's legal, shoe-goo is a good gap filler and adhesive(though I'd suggest bolts for anything spinning at high rpms)