So here's a dumb electrical question

If you are set on doing this, and I'm sure obvious to you, "go big," that is, lean towards bigger than smaller

What I would do is find a chart for ampacity (current) and make sure it's for 12V automotive use, not AC power.

Compare ampacity ratings of your 1/0 to 12ga, and add enough 12ga cables to total "at least" that much. I would not go by appearance.

If you can pull it off neatly, there is nothing wrong with that approach I guess. Downside for me, is you'll have a lot of wasted space with insulation.