1999-2006 Chevy Silverado / GMC Sierra Extended Cab Dual 10 Downfire With Amp Space Sub Box For 99-06 and 07 Classic GM Extended Cabs Fits Under Rear Seat and Subs Fire Down Holds Two 10" Subs, cutout size is 9-1/8" Has .70 cu.ft. sealed volume per chamber Amp shelf size: 18"w x 13"d