I'd recommend getting high quality marine grade wire if you can, and bigger is better on the gauge as long as you can install it easily. When I use the term "marine grade," I mean wire that is tinned copper throughout, has many fine strands instead of fewer heavy strands, and has heat and moisture resistant insulation. Ancor makes very good wire, a bit pricey, but it will last you decades. You can get it at West Marine or any good marine supply house. This quality of wire will be far more corrosion resistant. 2 gauge by itself is not overkill, IMO. I'd go thicker, myself.

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1987 W201 190D