Go to sounddomain check on some f150's similar to yours and take a look at the installs. It will give you a better idea of what you can fit first off. Then go from there. What are you lookn for in the sound. Cost limit? Theres alot to let us know instead of what should I get. Cause you will hear of amps that cost $1000.00 to buy and subs that cost you $500 ^^ apiece. so help us before we can help you :0)
Thats just the box though he still needs a sub/s and amp etc. He needs to know what he wants first (1) 10 (2) 12's ??? cant do a box with out knowing what you want.