Mystery Leak

[Dsm1957]

Hello folks, I have a good one for you. First let me give you the layout. I have 34RSBS. In the bedroom we have a closet, 3 shelves. Under this are the provisions for a washer and dryer. Recently, after a hard rain I noticed the bottom and only the bottom shelf was wet. The top two, the walls and inside the doors are dry. So... I did some checking, water lines underneath are tight and dry. There is a vent for the extra grey tank directly above on the roof. Everything looks good there. At this point I'm thinking wind driven rain? Any other ideas would be greatly appreciated. Thanks