> Salt water is also quite a problem

As a boat owner, I have had quite a time with salt water issues. Anything with an electrical current going through it exposed to salt and water is subject to serious, rapid corrosion. What you might imagine is "stainless" steel will, in fact, rust (unless correctly passivated and treated). The galvanic scale is not to be trifled with :). I can only imagine it gets exponentially worse the further below the surface you go.