Just as a side note, I installed subs in my car a couple of weeks ago, and ran 2 guage cable from the battery into the boot.
I found a handy spot to put the power cable through the firewall, its towards the top on the passenger side, there are already some wires going through it but its a very large hole, so I just cut a hole in the rubber surround.
The tricky part was feeding the cable through, because it was so thick and the carpet was in the way and stuff, I solved that problem by feeding a much smaller wire through first and tying it to the large cable so it was easy to pull through.
The easy bit was feeding the cable along the side of the car, because as I'm sure a lot of you realise, there are handy plastic channel things in the bluebirds for putting wiring along.
If anyone would like photos of the wiring install under the bonnet, let me know.