Aaron, try sticking a deflated basketball or football in the quarter panel. Place it in between the skin and inner fender. Gradually add air to the ball, and it will pop out the dent. Might have to move it around a little until you get it all pushed out.
This is one of the bigger reasons to not have the worse tires on the rear. Our hands are way more sensitive than our asses. We can more easily "feel" the front tires getting to their breaking point with our hands better than we can feel the rear ones about to break loose with our asses.