I had a similar problem in my first year with my Montana High County. My story is slightly different though. When the bedroom slide was out (rear bedroom) and the wind blew just right, the skirt under the bedroom slide would flop and make a banging noise, right under our heads in the slide.
The kitchen slide is the longest slide in the camper and I noticed it had upright supports and it did not flop at all. But the bedroom had none.
I ended up going to a Lowe's and picked up some flat 1 inch strips of metal, very stiff. It's found in that section with metal dow rods, square tubing rods, flat aluminum trim stuff.
The first thing I did was bend them so they would cause a very, very stiff spring action. I fit them, then cut them to length. I then drilled a hole in each end and attached on the back side of the skirt with self-tapping metal screws.
That took care of the flopping in even the strongest wind. It was easy to fix, but it did take some time and lots of measurements and a bit of trial and error to get the right amount of bend in each "spring" to make a very, very tight fit, yet still fit the space without bulging outward.
And of course, I had to work with each support separately, and attached one before working out the next one. It took a couple days doing it in the evenings, but the end result has proven itself. It's been over 4 years now, and we've never heard the banging again.