Solar Panel Mounting?

Hi All, I'm getting ready to replace my one original solar panel with four new ones. The roof is a loose fiberglass skin and feels like a thin layer of thin plywood underneath. I'm thinking it would be impractical to find ribs to screw the mounts into. Are the brackets just fastened into the plywood skin and plywood with wood screws? And on panel locations: the original panel is on the center-line just aft of the middle A/C. I'm planning to put one in the same location, and

Ok, here's what I wound up with. I used the Renology extrusions on the panels and made some 3" long brackets from 1/16" 2x2 AL angle for mounting to the roof with VHB 4950 tape. This makes one $30 Renology kit work for 2 panels, plus my home-made attachment brackets and some additional hardware. VHB 4950 is what AM Solar uses. I was concerned that a thick 1/8" extrusion would have no flex and might be too stiff to work with the VHB 4950 tape as the roof surface flexes. VHB 4950 tape uses 3M