The top wooden plate is attached to the tire well tub with fiberglass. I cut the rectangular hole in the plate (it would be a circle(s) if I kept it flush to the floor, but the woofer was too deep for that and I wanted it to match the amp rack. Working inside the cutout, I applied a generous bead of strand-impregnated fiberglass (Kitty Hair) to seal the wood to the glass tub. Did this make sense? BTW, that crash pic is down right depressing!