Have a good think about what your trying to achieve, snot too hard.
People use grounding kits to avoid different qualitative earths in a engine bay... so you reckon earthing the battery at the rear chassis is good enough?....
Ppl do, but personally (man, friends say i give too much away) you need to run a earth to the engine bay. Not as thick as the power cable, 4G say.
Iv seen so many issues caused by crap earth's, for something so simple, ppl seem to forget it (even if its not apparent, its causing them issues)
0/2G to the front, 250A fuse (should survive the starter motor drain) earthing kit in the bay. Run the cable under the car, or inside depending. ( I prefer inside)
Take the time to wack in a kill switch. Simply popping it, instead of removing a battery terminal is a god send when working on your car.
I tend to over engineer everything, specially when its mission critical; You can decide to make it as simple, or as extravagant as you want.