Drilling through the firewall

I need to drill a 1" hole through the firewall of my '06 for some 1/0 awg power wire (for stereo equipment). What's the best place to do this on the new mustangs?

From the inside, it's difficult to tell what a good spot would be since there's so much padding and insulation directly behind the firewall. From the outside it's still tricky to tell, I don't really see any factory grommets that would work.

Also, if anyone, knows this bit of trivia, is the spare tire well a solid place for the amplifier ground? I'm taking my spare tire out and mounting my amps in there.

Thanks for the replies. I'm not worried about the missing the spare tire since I have 24 hour road side assistance and I just drive the car in town. I have friends and family who can bail me out if I need them to. In addition, the removal of the spare tire and jack should help offset the additoinal weight of the stereo equipment I am installing.

I only ask if the spare tire well is a good place for a ground because some parts of the car seem to conduct current better than others, and choosing a poor location can lead to ground noise. Just wanted to know if anyone had tried that particular spot before I started drilling holes in the car.

My car is a manual, and I will try the spot between the battery and the engine, using caution not to puncture the refrigerant line. Thanks again for the help.

-KAUS