Mine is very similar to this one.... http://www.bhphotovideo.com/c/produc...roof_Case.html
I have never shot from a Jet Ski but I have shot a lot from a boat, from the bank and a media tower. There are plenty of guys on here that shoot wake much more often than I do. I shoot Aperture priority 95% of the time for everything. Aperture, I generally shoot two stops from wide open and keep the shutter faster then 1/1000 but I can get away with much slower speeds if I am shooting my 9 year old daughter. My ISO is usually 100.
I may use the bag underwater this weekend using a 5D M2 and a 16-35. It is a lot of fun, This was with a 50D and a Tokina 11-16.