If you already have 2 12's and a 10 in there and it is not loud enough then the enclosures are not built right. With the right enclosure those should almost knock the wind out of you. The trick in the back seat of a truck is to rip out the bottom half of the seat and build the box to replace it. Then you just use the seats upholstery to make it look stock. The people in the back don't have a great seat, but they are in the back so you aren't trying to get any from them anyway. Just keep the girlfriend and cute girls in the front seat and make the friends ride in the back.
From my experience with about 6 years installing show systems on the side, speakers are only as good as the enclosure they are in. Bandpass systems work great for large air spaces because they are tuned for it. Work great in jeeps with the top off or in the store. Ported-tuned boxes when done right are great for any vehicle, they are tuned to that vehicle so they should be. This is much more of an art than anything else. It takes someone that really knows what they are doing to get the best sound. A really tight sealed box is incredible in a truck. They are also easily built at home by someone that isn't an audiophile. No one can argue that JL would be better, but you have something else so the best thing to do is to build the right box for what you have.
