if you build it you could easily fit 6 to 8. 2 facing foward, 2 facing rear, 2 facing inward, and 2 facing up

thats enough to make ya crazy. the sound will suck but it would look tight. but seriously, id say put 2 12" facing inward inside the truck from each side. itll give you a nice overall bump outside the car. but if you were really going for something good just go with 2 really high powered subs n amps