I have the Window Max installed on this side. Keeps rain out with the Fantastic Fan on max. the Window Max screws into the window frame, not the trailer wall and is a fairly easy install.
You will see above the window a strip of standard vinyl J channel that I installed above both side windows
and over the back door to catch rain coming off of the roof. I attached it with some 3M 'Pretty Darn Sticky"(I forget the part number) double sided tape. Works OK in light
rain, but not in a storm. If you think this will work for you, I would extend it a bit further beyond the window frame. It would work better over a true vertically mounted window. It does do a good job over the door.