I needed a simple RV Vent cover for our RV, but didn't want to buy a full louvered vent. This is 111mm or 4.37" in diameter and goes into a standard vent with a clip. I believe this will fit 6.5" diameter RV Vents.

I included a small clip sample so you can ensure it fits your vent, before printing the full cover. In the photo, you can see it took a number of tries to get it just right!

I printed in white PETG as the RV could get warm in the summer. The arrows show you which way to slide, and which way to move it to release the clip if you want to take this off completely.

If you make one, please post a photo of the make.