hey guy....i didn't read all the advice, so my apologies if i repeat others words. i DO have first hand experience with this sort of set up. here is what you need:
1. run 4 or 5 gauge from the battery to the amps, put in an 80 amp fuse or circuit breaker in line close to the battery.a hint....go to a welder supply house and get the stuff much cheaper, less than half price, but no pretty colors.
2. divide the power with a power divider block just before the amps. use 8 gauge, or whatever it is that the normal power wire is, i forget the gauge.
3. use an optima battery, red top.
4. if you find that you are draining the battery (i doubt it), buy a capacitor for the bass amp, that's the one that sucks your battery dry!!!
i am running a rockford fosgate 200 IX on my sub + a JL Audio 300 watt amp on my 4 corners, no problems, and i'm not even using a capacitor. i never have problems. this system was in my cj7, with stock alternator, and now it's in my 1965 Rambler Classic with a 55 amp alternator.
any questions, hit me up here, or at jeepfun4u2@yahoo.com . good luck.....Rob