They have a large round screen on the inside (the interior ceiling side) to keep bugs out. The screen has a downside, though. It gets dirty with dust in the air and periodically needs to be removed and cleaned. The screens are held in place by about 9 small screws all around the screen's edge. You can get a pretty good crick in your neck and really tired wrists removing and replacing the screws.
Again, because I'm lazy, I keep my eyes looking for the better mousetrap, and I found it. The original, screwed in screen can be replaced with a snap in screen.
You remove the original screen, with all its screws and toss it. The new, snap in screen replaces it all and is easy to install. There is a little notch on the screen edge you can hook your fingernail in and pop the screen right off, clean it and snap it right back in.
You can find the screens at Camping World or other RV supply stores. They come in a 2-pack for about 20 bucks. My neck and wrists are happy.
Thanks for reading. Please feel free to post a comment...they're free!
PS: I now can post pictures on the blog again. Evidently Blogger and Picasa have made up and are working fine together again. I don't know what happened, maybe the threat of a hammer had something to do with it? ;c)
Anyway, I put a couple of pictures in the Battery Fill post if you want to take a look.