Late to this conversation, we brought our 2015 same model home a couple of weeks ago.
The switch is HIDDEN behind the other parts of the water heater. Turn you head about 90 degrees, bend down and you will see it.
One of those "once you know where it is, easy to find" things, but until you know exactly where it is, you will never see it. LOL
2015 32 Foot Rockwood 8289WS 5th Wheel
2013 Chevy 3/4 Ton TV