Rear Window Water Leaks

I had exactly the same problem with my 2006 Crossroads 5th wheel. The rear windows which were fixed and would not open had a channel that would fill up with water and on extreme conditions would run down to the carpet. I fixed this problem myself with the help of some black silicone. I simply ran a bead of the silicone all around the outside edge of the window where it meets the rubber gasket. I was careful not to use too much silicone and then gently smoothed it down with my finger. This was a few years ago and I have never had another leak no mater how much rain falls. The black silicone and black rubber match and unless you look really close you cannot see this simple fix!!