Here is what I came up for my storage. Definitely not secure.
I first did the http://www.wranglerforum.com/f33/che...ks-215074.html
mod. This is a great mod for the 2-door JKs with the rear seat removed.
I then mounted the below box using the rear set hold-down loops. This is the box I used: Amazon.com: GSC SL3500 Storage Locker, Black with Red Latches: Home & Kitchen
It looks gray/grey, but is is really black.
I used turnbuckles to hold it down. The turnbuckles I used have a loop on one end and a hook on the other. I also used a J bolt/hook bolt to go through the box.
I used some flat aluminum on the inside of the box to spread the tension across more of the box in order to keep the nut and smaller washer from pulling through the plastic.
On the back side of the fire extinguisher mounts, I used some more aluminum strips, again to spread the tension across.
I finished it up with some auto carpet hot glued to the lid. That should keep small items from instantly sliding off. The carpet works good with hook/loop tape also.