Jeep did have an optional trunk compartment
behind the rear seat that was lockable with the tailgate.
Most Rio Grande's had them and some Sahara's.
Those are too low to fit any sort of drawer toolbox though.
If you don't want to buy new tiedowns, you can reuse the ones up front. (hopefully, you've seen them.) They're between the door openings and the seats. These were used to store the rear side windows as well as the windshield supports when you lower the windshield.
