Grommets or bulkhead connector for trunk mount battery?

[Rileys68Camaro]

Which do you prefer and why? Is one brand better than the other for these parts?

I have the MAD Enterprises kit, and a Painless wiring harness. He uses 4(I think) guage for the battery cable, is that good? It's smaller than normal though.

EDIT: The 8ga wire is a primary power wire, not a battery cable. Mark at MAD recomends the 1/0 or similar sized for the main battery cables.

Sorry for the confusion!

But I still need opinions on gromments or bulkhead!