I've picked-and-plucked the foam in a Storm Case model iM2500 (the largest carry-on size allowed in an airplane. it's actually smaller than the bags that many people carry on, but I decided to be conservative, adhering to airline-published dimensions.), and it fits all of the non-housing camera gear I need for a typical underwater photo trip!
Packed Storm Case iM2500
In the case, I can fit: Canon EOS 1Ds body, 2 x Canon D60 bodies, 100-400L IS, 15mm full-frame fisheye, 50mm macro, 100mm macro, 28-70/2.8L, extra 1Ds battery, two extra D60 batteries, and a CF card case.
Not bad. I'll have to carry a flash, lens cleaning supplies, and chargers separately, but I had to do that previously with the J-1 as well. Now I can carry all of my stuff onto a small boat without worrying that my equipment will be destroyed. :)
Oh, and I highly recommend Cases4Less.com. They will beat any advertised price by 5%, and I have had nothing but excellent service from them.
Unrelated: Congratulations to Dave Patchen! His photo is photo of the day at Steve's Digicams. :)