I own a Danuu cover for my AI. They're extremely strong and well designed, and in my Opinion a must have if you plan to keep the boat outdoors for the season. It's made of a very thick waterproof UV resistant laminated canvas/nylon material. The best size for an AI is called the "Dude" and perfectly fits the AI with or without the amas attached and folded against the hull. they go for around $160 if you order it from their website and believe me they're worth every penny.
http://www.danuu.comI think Hobie actually sells Danuu covers with the Hobie logo printed on them so you could probably order them directly from your dealer, but I don't know if it's any cheaper to buy one that way.