I have ever had an issue with wind as it relates to my slide toppers. Typically they will not flap if adjusted correctly.
My grandfather used to say "You never know what will happen . . . until it happens!"
I saw a micro burst wind blow through St. Vrain State Park (Longmont, CO) that blew almost every slide topper off of every camper in the campground . . . not to mention every awning that hadn't been rolled up.
Ironically, the park rangers drove around a few hours earlier in the day to warn everyone of the high wind warning and to put their awnings away!
Funny thing is that hardly anyone (other than me, of course) heeded their warning and left their awnings and slides out!
Happened on July 4th, 2014.
I was planning on getting a slide topper installed on our previous 2013 Heartland Trail Runner the following week . . . but called up and canceled after I saw what the wind did to all of the RV's in the park.
Even though the weekend wasn't over yet, most of the RV's left the next morning after that.