88-98 Gm Ext. Cab 2-12'' Ported Poly Subwoofer BoxFits 88 98 Chevy Gm Extended Cab . The hardest hit sub box for the Chevy Extended Cab Armor Coated With High Pressure Polyurethane Bed Liner Material Increases The Base up to 4 times , stiffens the wood and no air leaks 2 12'' Speakers Front Firing Ported System Air Volume 1. 40 Cubic Feet Per Side Mounting Depth 7'' Material 5 8'' M. D. F Also Fits Extended Cab 3 Door . Dimensions: 59" x 19" x 15"