If you look at Cummins' pic, there are pins that hold the cover down. Taking these pins out allows the cover to pivot away from the vent cover itself for cleaning. These are very nice add-ons, and four of the original vent cover screws are used to hold the retaining clips for the cover.
You have to be careful in buying the cover--the normal covers will not work over a Fantastic Fan. As pictured, a Fan-Tastic Vent will work best over a Fantastic Fan.
There is also a Maxx Vent, I believe, that will work over the fan vents.
They do work well for ventilation during a rain event.
Joe