Problem installing Solar Panels

I have very limited space to fit the panels. I don't think I would be able to fit both sides of my panels right on the studs, but that is a good idea running long pieces aluminum into the beams. I still don't understand why I am not feeling any plywood under the rubber when I screw. It should be 3/8". I can see partially the plywood and rubber roofing material in the vent whole.