0 gage wire

Due to the thickness what is usually the best place to run it to the trunk? not on any car specific and i do know that all cars are different. But from previous experince what is the most common place to run 0 gage wire to the back of the car without noticing it.

I put amps under the seats all the time.  I have my amps under the seats of my car right now.  But how you got that from my original answer I don't know.

No, under the door sill is not an option for large cable.  Down the center often works.  Remove the center console and the seats for easy access.  Or mount the cable to the inside edge of the door sill with cable hangers and let it show.

If the wire can't tuck it under the carpet next to the trim panels, I usually pull the seats and console and run it under the carpet that way.

Really all comes down to the seat that we're talking about. In trucks and SUV's, one of the first places I check for mounting locatons is underneath seats. As long as there's a good 1/2" clearance above the amp and it's free air on all sides, it's a perfectly good mounting location. I wouldn't consider doing something like this under the back seat of a Civic though.