Amp Walls/ racks! Lets see them!

[EarmarkMarine]

A couple questions...

What grit sand paper do you recommend to sand the fiberglass?

Would "3M/1 gal. Bondo-Hair long strand fiberglass reinforced filler" from Autozone be a sufficient product to use to attach the board to the fiberglass?

Try 80 grit or courser. Just enough to scar an otherwise smooth surface to get a good bond.
Anything with fiberglass strand has some structural integrity and good adherence unlike a plain body filler. And, mix in a polyester resin 50/50. Don't forget the catalyst.
If its the hull surface use intermediate blocks and not the board/panel direct.

David