Are you referring to when the trailer is set up for travel or setup for campsite use.
Water intrusion can be a major problem over time. Is it possible the trailer was put away when it was wet? Can you describe the water intrusion a little better - to you have fold down or slide out beds where the water is intruding. Is the water intruding somewhere else like the trailer body, then ending up here?
If the panel frame is not closed correctly, it might need adjustment or something can be causing the panel from closing properly. These are some more things to check.