Something to think about: Go search online for top-dollar bass guitar amps/cabs/speakers. You'll find that the ones with multiple speakers rarely us bigger than 10" Guys who make their living off the sound they can make know that bigger isn't better AND that bigger isn't louder. I have personally witnessed an 2X10 David Eden cab absolutely shake an entire church foyer (about a 100'x100'x80'...much bigger than your truck interior) And as I guy who plays bass, I can assure you that it was the best sounding setup I've ever heard live. (just a straight power amp, Graphic EQ, an old Ashley Compressor...and a G&L 5-string)


something to note also is that these 12 and 15 inch woofer often outshine the smaller woofer at frequencies that are so low you won't be able to hear them in you truck cab. A soundwave has to complete one full cycle of its sine wave before it can be heard. Some low frequencies can be several feet long. If you're speaker is only 4 feet from your ears you simply will not hear any frequencies that are below that 4' mark. Feel it yes, hear it no.