Here's what I did when I first bought the Jeep.

The 3rd row was wrapped in plastic and hauled out to a shed.

I built a framework from pine. The wedge shaped area holds a floor jack. The lid is plywood with matching (well, a close match) carpet stapled to the lid. I left the original jack storage because other stuff fits there, and it's part of the rear HVAC system. The holes in the 1x6 pine are for the heating vents to flow.