I just use epoxy putty. Sand the bulkhead edges about an inch in on both sides and I pencil mark the location of the bulkhead and sand the inside of the kayak too. The back hatch is easy. I wet out the open grain of the bulkhead and whack it in so it stays in place. I just use my finger with a glove and run a filet on both edges, working in the back hatch for the back side.

On the front hatch same procedure. Since I have an ocean cockpit, I tape a plastic spoon on a stick and use that to make the cockpit filet since I can't reach it by hand. I have done this on many boats. It will never come apart - no need for glass and the filet can be quite small. Just seal the edges with a tiny corner of putty. You can use a drop light and mirror to see your work on the insides where the hatches are.