I am curious where the best place to ground the amp would be if it is mounted in the trunk? It seems that all of the painted surfaces do not ground. Should I rub the paint off of an interior surface to make a better connection or what.

I grounded all of my amps in my car to the rear right strut tower (doesnt matter could be left or right). I took off one of the bolts and sanded around (get all the primer off) it so i would have the most solid connection.