I just got a Blackburn seatpost rack, which came with a decent Nashbar bag. However, I need a trunk bag that I can carry with me when I run errands. I really need it to snap on securely and come off quickly without having to undo a bunch of velcro straps. Topeak has one that hooks a plastic wedge under the front end, while using a springloaded latch on the back. I just don't know if it will fit my rack. Basically, I want a bag to carry library books and DVDs, lunch,etc, with the option of a handle or shoulder strap, that won't slide around on the rack. Pictures would be helpful, if you have them. Thanks!