I built this specifically for the 8" Pioneer or Premier shallow mount subwoofer (free-air) and fits into the jack cover. Mounts in tight bolting into the jack bolt location (bolt and washers included). Does not vibrate once mounted with subwoofer. Carpeted to match the hatch panels. Made out of 3/4" MDF with 1/4" aluminum mounting bracket.
$55 shipped.
I can take pics of it mounted if needed.
$55 shipped.

I can take pics of it mounted if needed.