There are many past threads on covers for the MP3, but I wasn't satisfied with the choices. I wanted a waterproof cover that I would not have to worry about melting when up against the exhaust. I ended up getting a half cover by Nelson Rigg (http://www.nelsonrigg.com). The cover fits into a small bag that I can easily put in the top case or under the seat. Completely waterproof, will shield the electronics if it is sitting out in the rain, and has complete ventilation because it is a half cover.
The size I put on is the XL. I chose it because of the top case on the back. Here are the dimensions of the various sizes as given to me over the phone (not available on website):
Large: 78" length, front width 41 inches, rear width 20 inches
XL: 84 in length, front width 51 inches, read width 29 inches.
Pictures follow.
