are you sure that it is a panasonic amp? the gm-x742 is a pioneer 1, 2, or 3 channel amp. you could bridge it down to 2 ohm's if you had another 12 W-0. the JL 12 W-0 takes 125 watts RMS if i am not mistaken. if you bridge the amp down to 1 channel it should sound nice. as far as the box goes, if you listen to alot of rock music you are going to want a sealed box. a sealed box is ideal for that woofer. most woofers tend to last longer in sealed boxes. sealed boxes put out a cleaner, crisper, and punchier sound. but they are not as loud as other types of boxes. when it comes to sealed boxes, simpler is better. a square is the best design. i know all of your friends have their woffers facing the back of their trunk, but if you turn it around and face it toward the front of the car, not only will it sound better, but your trunk will rattle less. if you listen to a little rock music some techno and some rap, a ported box will be louder and boomier, but will not be as clean and crisp as the sealed. if you only listen to rap, then you can get a bandpass. bandpass is the loudest, but it cannot play the complex bass tones that are found in most rock songs. with fast, complex bass the bandpass seems slow and muddy at best. it will how ever go BOOM pretty good. as far as wire goes for that amp don't buy anything more expencive than 8 gauge power and ground. if you really want to you can buy $40 RCA's, but unless you will be using it for competition you really only need the $10-$15 ones. remember don't run power and RCA's on the same side of the car. if you want,
www.jlaudio.com has some potential box designs on their site. let me know how it turns out.