We have had the same experience as DK ... finally we got the second vent cover (MaxxAir Fan Mate Fanmate) installed on our new EB. We really missed not having the second VC on the last AS but it would not easily fit due - to the solar panel installation.
Do we like and use these ...YES all the time! They are durable as well as functional. We bought a white for over the non-sleeping area and a black for over the sleeping - to mask out much of the light in the morning. They are great - allowing continuous ventilation without worry or power requirements. We too lost a FF vent cover on an SOB while traveling in the rain ...what a mess. The Maxx-Air Fan Mate "over hangs the open FF vent and makes that nearly impossible now. As far as restricting opening / flow of the FF ... I doubt that you would ever notice any difference! Of course, YMMV - one of the best $$ that we have spent - this is now the third trailer that we have used the same Maxx-Air Fan mate vent covers on...easy to install and easy to remove!
~~~~~~ mefly2 ~~~~~>>>
AIR 44105 /WBCCI - formerly 2015-1; Yamaha XT250
:>) ducts are now in a row w / 2015 ducted air :>)
* 2015 Duramax 2500 Diesel * Honda EU3000iS
<>2015 International LE Eddie Bauer FB25<>