Not sure if this would help being I'm a electrician, but if you check resistance from the two points and have anything 0.4 or less that's a good ground.
Simple I would like get ideas as in what's the easiest way to run 4 power wires to the back, and see cargo area installs I have plenty subs so I can do just about anything, what has worked better for you? I'm not a numbers type of person. Thanks