should go in the sound forum...
but, to answer your question:
the rear seat bottom unclips when you pull up on it, giving you access to areas you can drill through to run wires to the trunk if you can't find a factory hole. My amp is wired with 10 guage wire from the battery on the right, and runs to a ground screw I drilled over on the left. I ran the RCAs from the HU to amp under interior door sills, then under the carpet to the hole from the backseat and into the trunk.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>