if you make the box 35 inch long, 14 high, 6 deep at the top and 11 deep at the bottom a single 4 needs to be around 13 inches long but make sure to keep that port around 3-4 inches off of that side wall..this gives you a tuning of around 38 hz which is perfectly fine for this truck..ive had boxes tuned into the 40's in this truck and could still play into the low 30's lol 38 is damn near perfect...anymore questions just lemme know..also your back wall is going to flex like a bitch.. so plenty of sound deadner as well as taking tennis balls and shoving them between your cab and bed will help alot..i know its ghetto but it works lol that or take self taping screws and getting some little 90 degree angle brackets and screw em to the box and then to the back wall...both help