caulk for CD kayak

I have an old Current Designs Equinox which I am replacing the D-rings and straps on the rear hatch. Rivets were used on the original installation, and the replacement kit I got from CD uses nuts and bolts. What kind of caulking compound should I use? Is a marine grade caulk required? If so, can it be had at Home Depot or do I need to find it on the web. Any paddling shops are quite a distance from my house. Thanks.