Don't drill. On the back side of the cab, towards the bottom, on both drivers side and passenger side, there's a rubber plug. You'll need to remove the rear panel, then Remove the plug, drill a hole in the center the size of the wire you're running, then cut a slit from the outside of the plug to the hole you just drilled. Once you've run the wire into the cab, slip the plug over the wire and reinsert it into the hole. Seal it with silicone and you should be good to go. That's what I did when I did the stealth XM antenna mod. Works great.