I really wanted to make my security trunk, but broke down and bought the Bestop Instatrunk instead. I believe there are two versions for YJs - one is plastic and one is steel. I bought the steel version.
My notes/thoughts on the Bestop:
1) It's pretty heavy and easy to install.
2) I marked and then pre-drilled the screw holes to about 3/16 and then the self-drilling screw did the rest - figured I would get more accurate screw locations this way.
3) the weatherstripping that they provide is about 2" too short. (the gray weatherstripping was included, and the black on the end is what I had to add)
4) I removed the carpet from my YJ, so there was a 1/4" gap on both sides of the Instatrunk.
5) I used some weatherstripping from Lowes to seal up the sides and bottom of the Instatrunk. I thought about using 1/4" x 1" aluminum from Lowes and sealing it up with RTV, but the weatherstripped was cheaper and easier and worked really good.
6) It isn't watertight, but I don't drive my Jeep in the rain -at least not intentionally
1) Add a little push pin switch and LED light (both from Amazon), so the light will come on when the tailgate is open.
2) Add an Accessory Power Outlet, so I can power a phone charger securely, run an tire inflator, etc.