It looks like a light switch, maybe to an outside scare/night light or an inside main light.
You might can turn your first light when enter the RV ON at the fixture itself. Now use the switch to see if it turns off the light. Many RV's are set up with this, so you can turn off the main light when entering exiting the RV in the dark, without having to fumble around finding the light fixture.....but you have to have the light kept on at the fixture itself in order for the switch to control it.
2011 Flagstaff 831 RLBSS
Hypochondria is the only illness I don't have.