For a 1990 Chevy ext. cab pickup. I was told this be Michael Jones. Build box as large as can and 165" port area per sub 7"-9" long port for 2 15" DD 9515 subs . If could would rather use 15" Fi BTL's. Area behind seats comes close to 18 cubic feet internal box area. If have a different recomendation for box design I'm willing to listen. Looking at using 2 Memphis 4kw amps and 16 volt charging system.