I use the plastic pieces and have the black bestop. Mine only flapped with windy days... I fixed it by adding a piece of pipe insulating foam. (the kind that has a slit on one side that slides of pipes.) I cut it size and stuffed over the center sound bar (4door). It raises the top off the bar and no more flap even at 80mph and windows down....

 

I know in th epast I have seen the arched cross bars to help keep the top from sagging. This would be great for when it is sitting parked in the rain. I have to reverse quickly to throw all the water over the hood to avoid getting soaked from the side. Anyone have these for the jk yet.