Re: SF Bay - how long do you get out of Pettit Trinidad SR?
I think a lot depends on how often you clean your bottom, and how aggressively.
With two coats my bottom lasted around 30 months (South Bay)---I stretched it to 34, but the last couple of cleans were not that effective. Now it is repainted, I am initially using a hand towel to clean it - I'll move to something more abrasive later!
BTW, brace yourself for sticker shock when you do repaint - my recent job was way more expensive than my previous one. Like almost 50% more! Damn I wish my salary had gone up that much in 3 years.....