First off, "ground" by itself is ambiguous, implies PE protective earth.
Negative return for all DC circuits should be at the same reference potential, aka "common reference".
This is always done via connecting ("bonding") the negatives to common **chassis** reference points aka "chassis ground" at several points including of course the main frame and engine block.
AC circuits should **not** be bonded to these references, and when connected to shore power, bonding to PE should be **only** at that one single point. Get a professional to sign off on those circuits.