If you want a cleaner installation without having bulging wires out of your carpets, you can run 2 4AWG wires to the rear. pretty much same throughput, and easier to hide, easier to get a hold of too.

 

zip tie it under the car and drill thru the trunk on my set up i did this I WOULD NOT DO IT 6hrs on a hoist
i would remve the seats then run under the carpets and ziptie at 6" then do your rca's and speaker wire at the same time

 

just drill a hole in your fire wall and put a rubber grommet in it run the wire through that then run your wire down what ever side of your vehicle the rca's aren't located your seat is probably one bolt to take out shouldn't take you more then an hour . 1 isn't that big , try some 000 welding cable for 2 1800 cca 4ds

 

just make a new hold run it down the middle of the car, under the glove box, if it has one in the center seats. this way the only bump u will see of cable will be in the back between the seats. i hope someone understands what im tryin to say here?

 

running it under your car just doesn't sound like its a good idea , its definitely the easiest and fastest (would only take me 20 minutes on the ground at the most with a floor jack )

inside is definitely your best choice just run it under the carpet and under the seat . or beside it .