For acoustic damping material, I like to use R11 insulation which is 2" - 3" thick, uncompressed. It often has a paper vapor barrier that I peel off. There are lots of other materials and products that might work but R11 has always worked well for me.You can put a grille over the port. A mesh or something like that would be just fine so long as it is non-restrictive.
For fasteners, I like T-Nuts for mounting heavy drivers or when serviceability is important. Wood screws are fine for about 20 tightening cycles but after that, the wood is stretched enough to tear through.