cx-7heaven 10+ year member
The dash don't be silent
Ground to actual frame, not body. Unibody cars have a frame of sorts as well. The reason why you want to frame ground over body ground, is 1) thicker metal, screws wont strip as easy. 2) this is the big one: every single switch, bulb, knob, motor or any other electrical part in your car is grounded to the body. This can create an extremely noisy system. The only thing grounded to frame is your batt and engine.