The water is coming directly out of the air -- not rainfall.
Folks, what happens is that the interior gets very warm and drives air out.
Then the lamp is turned off and the jar space cools.
It cools so much that it forms a vacuum effect and draws in moist air.
The vapor condenses at the bottom. The heat from the next cycle is not enough to drive off the water from the prior cycle.
Day by day, cycle by cycle the jelly jar fills up. Even WP gaskets are not enough to stop the condensate build up.
The only solution is to avoid this orientation -- or to provide a bleed hole in the jelly jar. A very touchy thing to pull off.
You'll see variation on this in cold and chiller boxes. You can slow things down, but the condensate just keeps coming.
BTW, treat your wirenuts as if they were below grade in such installs. Dip them in epoxy.
