[wingnut60]

There are several ways for water to get in even tho the slides are closed. Make sure all the seals on the slide faces (outer edges that face inward) are all intact--usually the upper corners tear quickly.
Sometimes the culprit is the lower horizontal molding that all the slides have at the bottom sides--check closely that there is a caulking seal all along the top edge of the molding.
Since the trailer is at home--strongly suggest that you make the effort during the next rainstorm to be out in the trailer and see where the water is coming from--or maybe make your own rain with a water hose with someone inside.
Hope you find a solution to the mystery....
Joe