You don't say what make/model water heater you have but if it's a Suburban, it's probably an SW6D__ model. On these models, the gas side is controlled by a switch inside the camper, usually on the "control panel" where your tank levels, lights and water pump switches are located.
The electric side is controlled by a switch on the outside of the water heater. You have to open the outside panel to see it.
If your model # has an "L" in it, then your electric side is controlled by a switch on the control panel (i.e., in this case, you'd have a "gas" switch and an "electric" switch on your control panel). They may be on a single panel like this one:
Finally, turning electric OFF does not turn propane ON, or vice-versa. The two are totally independent. You can have either one on, both on, or both off.
I've attached some docs for the Suburban without the "L" (i.e, no inside switch for electric).