I used light ply to sheet the bay where the wheels are. It is perfect for the job as said before.
Mscic, I'm not sure how you are using the deli tray? The bay where the wheel retracts is about 3" front to back, 5" wide, and 1/2 deep. Right now i'm just planning on leaving it hollow in that area. I was just worried that air would scoop in there and kinda of baloon the wing apart.