Old thread I know, but in case someone runs across it in a search...
My 93 as of today has the package tray removed and it's contents relocated to the area behind the hinge and shock mount. With the carpet removed, it's looking like I can get a box that's 38" wide and just over 16" tall.
I'll be building a 0.73cuft box that's 37.5" wide, 12" tall, and 16" deep (the mounting faces will be angled inwards to allow my nitrous bottle to sit in front of and somewhat between the subs.)