Vehicle electrical grounding

[WrenchMonkey]

I'm running some 0g cable from the battery on my Burb to the back, to run a small inverter inside, and eventually a small trailer winch.

It's got the stupid low-profile side lugs on the battery, so the positives all come off a separate distribution block, and the negative is grounded to (I think) the engine block.

Should I run a separate 0g ground cable all the way back up, as close to the battery as I can? Or just ground it to the rear of the frame, since the frame will have 10x the cross section that the cable does?

The shortcut will obviously be easier, but I've already bought the cable, so there's no extra expense at this point...