I bought an ATV cargo net (spider web type) and link it into the floor latch things in the back. I occasionally use that for lighter or bulkier items (shopping bags, umbrella, obnoxious children).
I also built a shelf from 1/2" MDF, plus a 1" pipe (use conduit strips to secure to underside, near to rear door) and 1" angle iron for strength (welded small tabs to it and then bolted underneath it widthwise). The angle has notches cut out of it to sit in the hoops that the rear seats latch to. The pipe fits nicely into the OEM rear cargo cover notches in the interior plastic. The shelf is strong enough to support a lot of weight and I have a set of e-track rings on each side to which I can attach a ratchet strap for hi-lift, gas can, toolbox, etc. Plenty strong. With the current design, at least one seat needs to be latched for this one to stay put safely.
I also have a flip top plastic box with velcro strips on the bottom. It doesn't move, but the problem is you can't move it (lol) and it sits under the shelf. This box has all my small spares, recovery gear, air compressor, etc.
