Rust on exterior, from inside drip rail/rain gutter.

I have a small gutter above the slideout on my KZ and suppose many brands have the same. Despite the trailer being stored indoors except when in use, the screws rusted due to poor workmanship. The gutter had butyl or putty tape that only served to guide water to the screws. I repaired using fresh tape in the right location, stainless steel screws, caulking and fiberglass repair resin. Photos