On our RW had same problem and I finally found the window was the problem. Check to make sure the small slot at the bottom of the window frame is not blocked or mashed closed, it is a drain and if blocked will cause water to back up under the window. Ours was caused by strange way water drained from roof down the side of the slide and I only way I finally found the reason was by standing outside during a good rain storm and saw the reason. Your windows are caulked only part way down on the sides and none on the bottom of the window. The rain water was running off the roof and down the side of the slide but instead of running straight down and off to the ground, it did a 90 and was hitting the window frame below the caulking. Caulked down the side of the window and a little bit around curve, leaving the rest of the bottom open to drain and this finally cured the problem...no more leak.