When my wife and I go off-grid camping, having a bunch of loose bags and camping goods rolling around the rear seat of the 4runner got old pretty fast.
In researching a solution (there are some great ones from goose gear and others) my wife told me she didn't want to remove the rear seats anymore than is easily done using the OEM setup.
We came up with this solution.. a custom built 1/2inch ply storage 'box'.
It has storage locations for my recovery gear box and some tools on the passenger side, an upright 20lb gas bottle on the driver side and it even contains a lockable cubby where we store electronic devices and cables.
Our clothing bags which are not heavy sit on the top of the cubby.
It even has a shelf for my wife to use for her 'extra' bags
!