The Quig

I recently bought a 94 z28 t top manual 6 speed 1 owner and it has a bose system but the rear driverside hatch speaker is nonexistent and the back seat speakers just whine and crackle looks like the owner before me tried to put some infinity speakers back there and f'ed up. Im thinking about a box from www.subthump.com the one without the t top storage and im planning on putting 2 jl audio 12w3v3-2ohm in it and then (forgot the name) some jl something cxi speakers that have a 50-22k hertz range in the front doors and rear seat speakers powered by a alpine amp that runs 50 watts rms x 4 channels and the speakers are 50 watts rms so I think that would work fine. still looking for a amp for the subs there rms is 500 watts And i know I will have to upgrade the car battery because it sat for 3 days and the battery was almost dead and I know nothing about car battery's so if you could recommend one that would really help. And im curios of anyone has had experience with subthump and im wondering if that sounds like a good set up im planning on getting the bass from the 2 12's and was hoping that the 4 speakers would provide good mids and highs. Im asking here because I have been to 6 car audio shops and the cheapest one wanted me to pay them $125 for a $70 walmart aftermarket stereo and charge me $70 to install it. the time it took me to install my current aftermarket stereo was under 3 minutes so obviously there not going to give me any correct information. My main concern for this setup is that it will A. Rattle my car to bits. And B. Be way to loud from the bass to enjoy the entire range of the music any tips are appreciated