Need Help on some questions about a box.

[Puppet Master]

Im making a false floor for my 2000 chevy blazer. In the box im going to put four infinity kappa perfects 12.1. Im going to make a brace for the vertical. But do i need a horizontal brace.

Im also putting plexiglass over the front of my four speakers. Is there a specific way to from making it rattle. What size should it be.

Should my box be ported or unported. Which sounds better.

Thanks for replying

[Puppet Master]

Also Would it help to put some dynamat at the back of the magnets