Isn't there such a thing as "marine" wire specifically made to resist corroding or some such shizz? I thought I read that on here. Maybe not.
Marine wire is tinned, not stainless.

It is also very expensive and unless your boat will spend 40% or more of it's life in the water, not needed IMHO.
Ralph, let me find out Monday if I can still get the Mercruiser wiring harnesses for $110 from a buddy of mine who runs a local shop, you will be money and time ahead....They are pre-jacketed and have all the standard wire colors for marine use. I put one of these in three of the last four boats we built and will never do it another way. You will spend over $110 on just the wire if you go the other way, copper is selling for well over $2 a pound right now as raw material.

I will let you know....On the positive side, they come with a canon connector at the engine, so removing the engine no longer requires a deconstruction, just a single plug.

GT