The best thing would be to face it to the back. you can turn the subs up a lot more without hearing the woofer actually moving or making the slap noise at high volume. a rear faced sub box whether sealed, vented, or bandpass has the best output because it bounces around more using the car as a sub box. The sound will carry for blocks if you leave the rear window closed and roll down the front two is you are going for public nuisance ticket. A singe twelve facing the rear of the car would be louder and carry farther than 2 10s facing up or forward. and 2 10 inch w0s would sound badass as long as you have the right size box in either sealed or bandpass, and run lots of juice to them, you will turn heads from hella far away.
go to any professional shop and they will tell you to face it to the back to increase the load. basicaly, POINT BACKWARDS, MORE BUMP, better low end response. you will notice a great difference inside and outside the car. if you get any RATTLE coming from the box stuff it with fiberfill or put insulation on all the walls of the box, you will get a cleaner sound and it will sound like a bigger box cuz it slows the bass waves.
