I have a 96 GT, and want to upgrade the sound system a bit. Is there any kind of panel that goes flush against the back of my trunk, or would I have to custom fabricate that? I think it would look better than just a box sitting there.

 

http://cgi.ebay.com/94-04-Ford-MUSTA...item45eb7e3904
$149.99 shipped.
This listing is for a Brand New ZEnclosures 1994-2004 Ford MUSTANG Subwoofer Enclosure
This Enclosure is available for 1-10", 2-10", 1-12", or 2-12" subwoofers and with round or square holes.

Hope this helps. I am sure there is more types of boxes. But I am lazy.