This complaint goes back to 2006, if not before. Here are some previous Threads on the issue.
https://www.montanaowners.com/forums...ad.php?t=16728
https://www.montanaowners.com/forums...ad.php?t=79358
https://www.montanaowners.com/forums...ad.php?t=30205
https://www.montanaowners.com/forums...ad.php?t=65105
Bottom line, there doesn't appear to be a good, neat, professional looking solution. A PVC framed awning (unfortunately the pictures are long gone - thanks TinyPic) or an umbrella (Golf sized stuffed between the awning and the slide) are the choices of last resort