Best place for a ground is to drill a new hole somewhere in the trunk, and sand around the hole. Make sure you have a metal connector on the end of the wire, not hust bare wire as its more prone to oxidation. Never use an existing bolt on the car as 99% of the time the surface is painted underneath. Caps can help with the dimming of the lights as they store powere in themselves and have the amp draw from them instead of putting more stress on the alternator/battery. If a cap is used, I wouldn't go less than a 1.5 farad, and that's really pushing it, but decent for budget builds. Stay away from low-end amplifiers as they tend to give off more heat in place or sound production. Ensure that you have the appropriate guage wire and distribution blocks to support the power and ground.
