If there's no switch and your RV has a rear window, there's another way. Mount a mirror towards the top of the window, angled at 45 degrees. Bring your camera inside and mount it on the wall, looking up at the mirror. Extend the wiring from the exterior camera mount to your new indoor one. That gets you a "real" mirror image. Put a panel over the old location to prevent water ingress.
A friend of mine, whose RV didn't have a back-up camera, rigged up a computer camera this way and saved the expense of buying a waterproof one. Since it was a wireless camera, he didn't have any wiring issues. He used a retired small lap-top on the doghouse to view the image.