I went through an existing hole that was plugged with one of those plastic thingy's. The hole was under the pass seat in good spot for my application. I then ran the wire zip tied up against the frame up to a "cavity" between the fender liner and the firewall along side of a factory wiring harness. Have had two different amp power wires run this way with no ill effects to speak of, however I don't ever go off-road or anything.
Btw, I took a punch inserted into the hole and then gave it a good twist towards the back of the truck. That gave more of a good transition flaring the front of the hole upward, and the rear half of the hole downward. After my first power wire was removed, I gave it a VERY thorough inspection, and you couldn't even tell it was touching anything.
Hope this helps!