I have a sedan and the rears were easy as long as you don't break the big rubber boots and plastic pieces inside. I pulled the rubber/plastic boots off and ran the speaker wire directly from the amp to the rears then sealed the boots back up making sure the plastic pieces had a small notch cut out and was sealed with silicone.
The fronts were a pain in the rear. I was going to run the wiring directly into the doors but we all know that is kinda hard. Instead, I ran the wiring from the amp to the area where the wiring harness enters the door jamb. I then spliced the wires and used the stock wiring in the jambs. Once into the doors, I spliced and used new wiring for the components.
It all worked well, in the Escape, I ran it all up to the front, behind the HU, and just tied it into the wiring harness using the stock wiring into the doors. Course this is on ly 4 channels of 45 per where as the Focus is getting 75x4.