I ran mine under the car along the fuel lines then up over the gas tank. Theres already a grommet in the trunk floor centered right behind the rear seats.
The best tip I can give you is to start in the trunk and go forward from there. Its easier to drop the wire down around the gas tank than it is to push it up. Once you drop the wire down past the gas tank follow these fuel lines to the front.
Then up the fire wall to connect to your fuse holder and battery.
Not sure if this is late, but I ran mine in my SE R through the firewall. But you'll have to drill a hole for it. The place I drilled mine was where the clutch would be if it were a manual ******. In the floorboard there is a little piece that pops out for this. Easy. Drill, grommet and go.