Thanks, the lexan was my answer to no wood, however after I started my project I found a board at West Marine that I think would have worked better.

I had a lot of trouble getting the lexan to adhere to the fiberglass and had to use a special epoxy for plexiglass and lexan. I had to build a device that would put weight on the mounting block and hold it against the fiberglass with some pressure. In the end I am really happy with the install and it sounds as good as I hoped it would.