This was one of my first additions to the LJ, it gets used almost as much as the tailgate handle. I used all stainless, a stud holds the chain as well as holding the shelf shut, via a simple wing nut. A lip around the shelf helps keep round stuff from finding the ground.
A tailgate stop is a good idea also, holding the gate open on an incline is a must. I made both for my LJ, neither were available from the aftermarket back then. On my LJ the plastic vent pulls out, easily allowing access to the center portion of the tailgate. The ends of the tailgate require a fastner with no nut access from the back, such as a rivet, which I used on my hinge.