JL Audio was working on one, their "Stealthbox", thanks to the demand shown by several members of XOC in a cooperative mass emailing effort.
It is not listed on their website... As of yet.
For more info:
http://www.xterraownersclub.com/cgi-local/ultimatebb.cgi?ubb=get_topic;f=38;t=000749
or contact JL Audio direct at:
Mailing Address:
JL Audio, Inc.
10369 North Commerce Pkwy.
Miramar, FL 33025-3962
United States of America
Phone: (954) 443-1100
Fax (General): (954) 443-1111
Fax (Tech Support): (954) 443-1108
Forgot:
http://www.jlaudio.com/ There is tons of info in this forum, if you have time read through it.
Hope this helped.
-Jeremy