I had extensions on 3 of the 4 corners. On the right rear the awning arm was so close to the end of the gutter an extension could not be used.
What I witnessed during a rain was the water would flow to the end of the extension and then wrap around the underside of the extension and flow down the side of the coach. This is the same concept they use for the gutter helmets.
Also, and I have noticed this with the current coach, the majority of black streaks occur around items such as window frames, the mounting points for the awning, and around the door which has a make shift rain diverter installed. Gutters and gutter extensions on my prior coach did noting to eliminate those black streaks.
Now, I am planning on putting gutters over the windows. One of my warranty items was a water leak coming in the bathroom window. The water was actually coming in the inside window frame and running down the interior wall. This only happened when there was a heavy rain or melting snow that accumulated on the top edge of the window. Having a gutter on the top of the windows would keep water from accumulating in that area and prevent a leak. On my coach the bathroom window had to be removed and resealed to stop the leak. Luckily there was a 9 inch snowfall while the coach was at the dealer for its warranty visit and the dealer observed the leak first hand.
US Army (Ret)
2020 Entegra Accolade 37TS
2019 Jeep Grand Cherokee Trailhawk (Toad)
FMCA - F432054