Cargo cover under canopy... does anything like this exist?

I got a canopy because I need to haul stuff in the rain that can't get wet. However, one thing I miss about my old hatchback (a Matrix) was that it had a flexible cargo cover panel that clipped in place over the "trunk" area. It was great for hiding tools, gear, shopping bags, etc. while I was running an errand or parked at a trailhead.

So essentially I want a tonneau cover inside the bed, under the canopy... if that makes sense. Is there a product out there that is kinda like this?

I'm in the process of building a plywood sleeping platform at the moment, partly to function in a similar way. It's coming along nicely so far, but of course 3/4" plywood and 2x4s are rather bulky. I'm thinking I could make something out of outdoor awning fabric, clipped to the inner bed rails?