After a day of the "Raindrops won't stop falling, GfIs keep tripping, blues"
I am reminded of a trick I learned too late.
When you make up a wet location box arrange the wirenuts so they point up and as high up in the box as possible.
"Raintight" ain't and they all seem to collect some water over time. If it collects in the wirenut you have problems.
I also like Dow-Corning 111 silicone grease to seal up the threaded plugs and covers. It is safe on all plastics and has a good dielectric rating. It is similar (same?) to spark plug boot grease.
It also protects aluminum so you can get those plugs back out without galling out the threads after they have been in the weather a while.
