I think what you are interested in is one of the Mark Pack Works underdeck bags. They make three models: The underdeck bag (which is the one pictured by the first respondent), the mini underdeck bag (the one in my photo--which is generally the best choice for size, and by far the most popular), and the micro underdeck bag. The mini underdeck bag is one of my favorite accessories. I wouldn't be without it personally. I used to sell a lot of them when I ran Eddyline's retail outlet, and the customers that bought them were universally enthusiastic. The reason the mini is more popular than the larger one, is that the larger one can impede a person when exiting or entering a kayak. I was always uncomfortable selling the large one except to people with small feet and tall foredecks. I hated to speculate on the idea of someone snagging a foot and panicing, and failing to exit. Ugh! We feature these in our website on cockpit customizing at kayakfit.com.