Our AF990, like AnEv942, has a vent cover the "almost" fits the exhaust vent pipe. When we bought it, enough water had blown in that the fiberglass below the vent had delaminated. I repaired it and have replaced the vent cover 3 times in 4 years. We keep it latched 99% of the time, even then when we get high winds the vent damper flap vibrates very loudly. After a period of time the damper splits down the middle.
I caught the last one before the pieces fell out and duct taped it in until I can find/make a replacement. I'm not spending any money on camco or valtera plastic as I've tried both and they are both a poor "sell it to mikey, he'll buy it" design.
But, it's going to have to warm up a bit before I go outside and figure out a replacement. I, like so many others on the forum would gladly pay a reasonable amount more for something that has a bit of quality in it.