Re:FRP Ceiling Installation Methods
Regarding Stainless Screws corroding:
SS should take a lot before it corrodes, but there may be an explanation that's not about water to explain it.
I've recently done some reading (So I'm no expert) and discovered the concept of "Sacrificial" related to metals, especially when Zinc (galvanized) is involved. Turns out zinc can cause other metals to corrode, so if you had some galvanized metal in contact with the SS screws, that may have been why they corroded.
The basic theory: The reason galvanized steel endures better than regular steel is because zinc is sacrificial to steel, which means Zinc will absorb the corrosion (until used up) before the steel corrodes. But when other metal are involved it's not as simple.
1. There is a hierarchy of metals. The least/most Noble (on periodic table) determines which ones are sacrificial which others. I don't have a list handy. You'll have to google it.
2. When dissimilar metals are in contact AND Zinc is present on one of them, it creates an electrical charge that accelerates corrosion.
So when multiple metals are in contact and one or more are galvanized, the most sacrificial will corrode 1st, and much faster than if no zinc was present. Maybe that was SS in Roadkill's case.
Personally I'm avoiding anything galvanized.