On my last trailer we had Mud Daubers building nests in every opening they could find.
Not this time! One of my first purchases was this Camco 42144 Flying Insect Screen - FUR 500, it fit PERFECTLY without even having to use the springs to hold it in place. As a matter of fact, I'm not sure I can get it back off, it snapped on over the vent.
So the first ting we knew we wanted to do was replace the ugly wallpaper type back-splash with something more like real tile. My wife found this nice peel and stick and it was so easy to do, we did it while camping. You can find the Peel and Stick here on Amazon