Jim--thanks to your posting about the window gutters, we picked up some black ones on our last journey to the states (at Camping World)
When we were on the first part of our trip (we didn't put them on until we were home and trailer cleaned) but a couple unexpected downpours with the 2 rear windows wide open--wet pillows on either end of the bed. We don't have opening windows at the other end, so I certainly like to keep these open..
Haven't been out or left the windows open at home to see how they work, but the 10 foot box did both rear side windows in our 17B quite nicely. You barely even see them.
Next weekend we are going away for four days, not that I want rain...but!!!!