Forest River uses the same vent manufacturers as everyone else, Camco or Ventline are the most prevalent. The sun beats them up pretty good. At the parts store where I work, we sell a hundred or so every season.
MaxAir vent covers do help, and they are a little beefier plastic than the vent lids, but the sun will still degrade the plastic and they are more expensive than vent covers. One advantage to MaxAir covers is that if you park inside or nose into the prevalent wind, you can leave the vent open a crack and vent the inside of the camper in storage.
When you go to the parts store make sure you bring one of the old covers. There are 5 different types of hinges.
