Attached pics for reference: Imgur: The magic of the Internet

I've got 2x 48"x"12" rubbermaid shelves, when I halved a 96" one. I kinda wish I could have gotten a few more itches width, but oh well.

I have a few things I need to figure out:
- How to reinforce the shelving - I think the weight capacity is fine, but "doubling the width" I have no integrity in the middle. I was thinking of SOMETHING like a couple of these mounted (even with just zip ties) diagonally which I'd suspect would provide all the structural integrity needed? https://www.homedepot.ca/product/pau...unc/1000149703
- How to hold the shelving - I was thinking of a shorter 2x2 (or what size?) up on the wheel well shelf, along with the a longer one at the back. I'd probably need something like this attached to wood and holding up the shelf, but would it hold it well enough? Something else that would be better attached? https://images.homedepot-static.com/...67-64_1000.jpg I'm quite sure I can't get a post on BOTH sides to sit right beside the shelf due to width+trim, but not sure how far apart it would stand.
- How to secure it - I was going to use the cargo tie downs near the hatch + those turn buckles mounted to the rear shelf post, but not sure how to secure the forward one. Was also thinking something that could push into the cargo cover, just like the cover's post but not even sure how to go about that.

The idea is to have the shelf height at roughly the height of the cargo cover.

Also, this is a temporary + non-permanent solution, something I think I'll improve on later and only be putting in the car for weekend trips and whatnot.

Any advice/guidance to help me complete the build?

may be able to help with ideas but without being able to picture how the back is getting loaded up makes coming up with a strategy difficult. what's going on the shelves and on the plywood?

Plywood will get carpeted, and then either used to sleep on with mattress or camping pads. It'll be in there semi-permanently, so outside of sleeping mode random gear and whatnot will be shoved there.

The shelf, idea at least, is to keep it more minimal weight. Maybe add bungee core/net to help keep things in place. In an ideal world, I'd also be able to move some things up there (backpacking bags?) up there during sleep mode, as they've be "above the feet" area.