Finding the right hole

Where exactly is the best place, a good place, or any place at all to pass a 4 gauge power wire thru the firewall on a 98 chevy tahoe. (must be passenger side only) Right now I've skirted the issue by going around the firewall and thru the door jamb where the rubber vent/wire flex hose is. Problem is water follows the power wire straight down under the carpet. I don't mind drilling unless there is some existing hole that will work. Nothing so far is obviously visible at first glance that looks accesible.

Take a look at where the antenna comes in on the passenger side. It is right by the top of the carpet, about 1' in. Just pull the carpet down and you will see the coax coming and a 2" grommet. enlarge the grommet hole a little and you will be all set.