hello,i assume your ford is not extended cab. in my opinion, you should look for subs with a shallow mounting depth, another words subs that arent very tall from the magnet to the top. look at 8's and 10's. your box will have to be tall if its gotta be small from front to back. you can always put some polyfill in the box to give it the sound of a bigger box. look at the smallest box size a sub will work in. protech 10's will work in a truck box .67 cubic ft. thats
small. its just a prefab sealed truckbox. if you would like to know where you could get these subs, write back with the title "more info from corey". if you solve your problem, good job,but believe me, i can help when it comes to subs,just remember, when dealing with the tiny space that you are, dont expect massive spl, but you'll have good sound, and some volume.