Chris, #3AWG is good. I would run it inside the car but outside is ok if not exposed to road debris and salts. One advantage in using wire is, you can 'train' it around corners and bends so it conforms with the body.
The main aisles in the DIF had steel tiles in the cement. The floor sweeper was going around the clock but if I stood in one place for five minutes and took one step away, the fly ash would show where I was standing. Man, that stuff burns if it gets in your eye. It also ate through the paint on cars in the employee lot outside. All the houses around The Rouge were black with acid rain and their brick mortar on nearly all the houses was loose and coming apart.
We used to get "Rouge rain" meaning, a lot of times it was only raining over The Rouge. You see my avatar with the smoke stacks... that was no joke. The Power House, foundries and all the steel operations; they all produced a lot of smoke. Yes, we had precipitators that caught most of the solid pollutants but it was a losing battle.
Another danger was carbon monoxide gas. It's odorless, colorless and our lungs absorb it 25X faster than oxygen. It's produced by UNburned gasses from any fire and it burns a pretty blue. CO is heavier than air so it settles in low places.
Coke dust is 99% carbon and it conducts electricity like copper. We used to open all the panels and control room doors weekly, just to blow the coke dust out. Many times an electrical panel would simply fry because it was filled half way with coke dust, short circuiting terminal strips of 250 Volts DC inside. - Dave