Originally Posted by overlander63
You could have a leak at the awning rail, plumbing vent, air conditioner, even the roof vent in that area, as well as the seal around the window frame.
And just to add to the fun
Water will run quite a ways in an Airstream due to the framing structure. I had one leak that was following a horizontal stringer and showing up about 10' behind where it was actually getting in.
IMHO the best approach is to start at the top and work your way down, cleaning and resealing as you go. One of the easiest and first things to do is replace the vent gaskets and screens.