I'll add that boats don't always sit at the same angle on their trailer as they do in the water... this can easily create places for water to pool, or enter, beyond condensation, that would otherwise ALSO happen.
My Capri 25 was dry as a bone in the water... and took on water on the trailer in the rain. Turns out the nose was up just enough so water didn't run directly off the coach roof, but instead ran along the hatch tracks, and dripped down below. I'd routinely have water on the floor below, ABOVE the bilge... Bilge would stay dry. Prior owner rarely had the boat in the water, told me it had a leak and he couldn't figure it out. I bought it from him and put it right in the water, and never noticed it, until I hauled for the winter. Then I went on a mission to figure out where it was coming from. A couple minutes down below, while on the trailer during a rain storm, and viola!