It all boils down to the wind direction. On my coach, 90% of the time when we travel, we do not hear the vent cover flapping. On a small percentage of the nights in random RV parks, we hear it making some flapping noises.
It never flaps while traveling at highway speeds. If you tend to stay in one place/position a lot, and the wind is in a common direction, it might be a bigger problem but for us, it is a minor noise.
Gary and Dee, Zowie and Bowie (traveling cat sibs)
2019 Cornerstone 45B, X15-605hp, Imperial, Spartan K3,
2013 Honda CR-V toad, Demco Excali-Bar II,
Demco Baseplate, Demco Toad Light system, 73 de W5FI