I'm a photographer and have had a long standing battle finding the right camera bag. I found one I liked and it will even hang from my rack, but not well. So after finally getting sick and tired of dealing with carribeaners, I bought some small parts out of the Ortlieb catalogue, and made some improvements. I had to do some fiddling to prevent heel strike, and really like the results.
It snaps on and off the rack in seconds, and holds on like glue.
--A