The roof of a camper can get pretty dirty, and requires periodic cleaning. The roof fans on your rig will need it too, and not just the outer cover.
Today, after a year and a half in the rig, we unscrewed the fan casing and Steve got up on the roof with some windex and the vacuum.
The casing is in two parts; one is clipped to the camper frame
and the other is screwed into the ceiling of the room. They are easy to remove but you'll need to be on some sort of stool. The four screws will give your arms a work-out.
When you pull it apart, you will see lots of bug corpses, dirt, and other organic matter.
Be careful handling these plastic parts as the small clips become brittle being exposed to UV light,
and can break. (This I know to be true.)
Into the shower for a spray of cleaner, hot water, and a sponge.
Inside the grooves you will see the same bug community as well as
possible matter left behind during construction.
Clean the fan itself and brush away cobwebs and other non-fan related stuff.
You probably have been cleaning the screens regularly, so these shouldn't be too bad.
All back together, clean, and ready for use.