I had totally forgotten about those pics! I wonder if that support bar thay have going down the middle is really needed?? I dunno if the bumper support bolt holes can support the entire weight of the car or not. I'll probably just jack the car up about 3-4 feet so I can keep the bumpers on while making the tray.
While I was walking through Home Depot I was look=king for other potential materials. I found 2x4 ft flouresent light covers in styrene, and in acrylic. Seemed too thin and brittle. I also found a 4x8 ft sheet of plastic pegboard. The holes could act as dimples? Anyway, pretty heavy stuff. Then I saw the vinyl siding. Lightweight, cheap, flexible by rigid when pieced together. A good candidate as long as the seams are aligned in the direction of airflow.