I installed a wall switch for my bathroom fan. Although my wife and I could reach it, I wanted to reach it while sitting down, for obvious reasons. The difficult part is routing the wire inside the ceiling and the wall. Every RV is different. You will have to find a way to run 2 wires from the light to the switch location, or one wire from a 12v source and one wire from the light to the switch.
It may not be easy.
Edit: While I was at it, I put in a timer for the fan and switches for the ceiling and cabinet lights, all in the same wall location.