Where is it getting power from? Did you make the rear 12v outlet? then have the wire going under floor mats and from there behind the seats?Figured I follow up and note that I opted not to go through the trouble with the C pillar (didn't really have a choice since I actually ran out of cable lol). Ended up routing it between the rear seats and the trunk and hand-shaped the wire to be neater. Gets the job done and at least it's less noticeable to me than wires hanging from the front.
By the way, pro tip for those considering dash cams and have a little bit of OCD, save yourself a wasted 3M sticker by taping the center line of your car before you stick on your dash cams..