Routing Amp Power Cable

I'm installing a Rockford Fosgate amp in my 1997 GT, and decided to follow their recommendations and use their wiring kit. It includes a heavy gauge power cable with inline fuse, which connects directly to the battery at the positive terminal. I've fastened the fuse holder to the top of the underhood fuse box, and now need to figure out how to get the cable into the dashboard. Obviously I need to drill a hole through the firewall big enough for the cable and grommet, but I don't know where best to do so. I'd like to avoid drilling through multiple layers of metal. I've tried to find where various cable bundles enter the passenger compartment, but they're all well-hidden. I've thought about drilling near the steering shaft, as at least that's a recognizable landmark, but again I don't know how many layers I'd be drilling through.

Any advice would be very appreciated.

Cool, thanks. Will try that.

That's a possibility too. As it happens, there's a small separation in the floor resulting from a bad jack / jackstand placement some time ago, which would suffice to allow the cable in. (Then I need to figure out a way of plugging the remaining crack.)

Haha. It was easier than I thought. If I'd known about the location of the clutch cable earlier, I wouldn't have had to ask.

The car is automatic, but it has a clutch pedal, and I've long suspected that a previous owner swapped out a manual transmission for the automatic. (This would explain why the speedometer is inaccurate as well.) There is a port for the clutch cable in the firewall, but it is plugged by a rubber seal. I simply drilled through the middle of the seal, using a bit slightly smaller than the cable diameter. Done.

Thanks for the help, guys. I still need to seal that bottom crack, but I think a few applications of silicone adhesive will at least waterproof the floor.