Then it's a total guess. If you can't figure it out and you have your hands on it, pretty hard to armchair quarterback this one. Leaks are tricky things. You could have a leak in a seal in the front of the roof cap and it not present itself until halfway down the coach. Water could be traveling from rain behind the outside trim piece that meets the floor and coming through, a bin door seal, around a window and inside the wall, etc. On our last FW, I had the smallest hairline hole in the sealant around a window and it presented itself near the floor a few feet away. Looking at pictures of your rv on line, looks like you have a window near the area.