Audio Systems: 1993 Cougar JBL Subwoofer, ford explorer xlt, jbl amps

Question
Hello, I own a 93 Cougar with the premium JBL sound system that came with a 6" sub mounted in the trunk.  When I purchased the car I could not locate the Sub.  I want to upgrade my audio system utilizing the Factory 85 watt amp that came with the car.  I just cannot locate where it was mounted.  My owners manual says it was under the rear deck in the plastic "Package Tray".  There is a black plastic tray mounted up there.  No sub, but there is a metal box that is there but I do know if that is the factory amp.  I tried to remove the tray but it is not mounted with screws.  Am I looking in the right place?  No one seems to know.  

Answer
the jbl factory woofer was optional almost $500.00
it was a single coil 2 ohm woofer or 2 6x9,a plastic box that mount under the rear deck and a factory single channel amplifier that mounts next to the jl amplfier

the unit looks like this but it is not the same

http://cgi.ebay.com/ebaymotors/91-92-93-94-FORD-EXPLORER-XLT-JBL-AMPS-SUBWOOFER-...