what would happen if you put a layer or two of a deadening paint inside a ported sub box, i know if its thick enough, it will take away volume.. but will it help for better sq or spl?
use carpet padding on 2 of the interior walls, like the top and the back, don't do them all. You want the sound waves to couple inside the box, but not cancel. If you can't find carpet padding you can find Poly Fill in sheets that you can staple up this should work decently as well.