A far more cost effective and long lasting cover for all of the outside vents can be made of common screen of the courser type that is larger openings than the normal screen wire but still small enough to keep the larger bugs out. Gnats we don't need to worry about but things the size of wasps/mud daubers are what we need to stop, so a stroll through a good old fashioned hardware is my choice, then cut and fit.
I don't like the sort most often seen because if they are easy to put on , they are also easy to knock off! Those sold for frig vents often do not fit well and leaves open gaps.
2015 Winnebago Vista 31KE on 2014 chassis