Using an abrasive on any track will remove any plating and leave scratches for dirt to collect. That surely hastened the demise of the tubular track.
I see that you live in the 50th state, so your situation may be like those that live near the coast on the mainland.
You can't do much about the effects of salt air. I don't think it matters which way it's blowing in. It's all around you.
Don't plan on using flex track if you go stainless steel. It just not malleable.
If you call Gargraves (Eastern US time), you will surely get the information that you need straight from the horse's mouth. They have seen it and heard it all.
You may want to check some of Garden railroad websites for some feedback also.
I can't help you on the Atlas, except to say that the product is solid rail. Nickel plating can be very corrosion resistant. It depends on the alloy. Same for stainless steel. There are different alloys.
Regardless, either would be better than tin plated rail that has been abraded.
There have been a few discussions on humidity control on the forum and some coast dwellers chimed in. Search the forum for "humidity". I think you'll find some useful comments from experience there. Some drift to equipment preferences, but in there are some coastal comments.
I hope some others help you out. Aloha.
