As a tech, and working on RV's, I have never seen a switch in a camper to control the electric part of the water heater. That switch you are referring to should be as described in post #2. The electric switch is always behind the outside cover, open it, look in the bottom left corner for a rocker type switch, and it's hidden pretty well.
Now before the argument starts and someone swears they have an electric switch in side for their water heater, I'm not saying somebody doesn't do this, but I have worked on quite a few campers, and never seen it, not even the 2012's we have on the lot.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT