I just bought a used EWA-Marine U-AXP 100 on ebay. It was delivered with an adapter ring for my 10-22mm lense. This sac fits perfectly for my 20D including the EX580 flash. I don't know if you can use a fish eye-but giving the fact that the adapters can be changed I think it'll fit...
I bought a used EWA off Ebay too. Wouldn't waste your money. If you're shooting off a tube and not going underwaater get a 1D or a 1dmkII with a 70-200 f2.8 L IS - they're waterproof enough to handle a tube. (Get some insurance too just in case!)
I just got the ewa housing for my 300d and like it so far. It takes a little getting used to, and you better get a squeegee or something to clean the water drops off, but it works much better than I thought it would. Word of advice... get a BIG tube, like a 3 man tube, it makes it soo much easier to handle the cam. Here are some shots taken from the tube.
Hey shelby.. are you still in Tupelo? We should try to get together one weekend and you can try out my housing, see how you like it. How big around is your fisheye? The port on mine is (I think) 77mm. I think the one Markus got has a 100mm port. Later Tiff