Water heater operation

[Oldflyboy]

Installed in the camper is a Suburban SW6DE water heater.

I have a switch on the master control panel that ways water heater and when turned on beside that is a red light that comes on for a little while. I think that is for the operations of the gas side of the heater. I can hear the sparking to light the gas.
On the outside on the front of the heater, is a small switch that just says on/off.
Am I correct to assume that all I need to do if connected to shore power is turn this switch on the outside on and the heater would heat electrically?
Would I have to turn the inside switch on at all?
The owners manual and the one dowloaded is not clear.
I guess the ga would probably heat it up faster then the electric would just keep it hot unless there is high demand then the gas would kick on.
Am I correct in my assumptions?
I yield to those in the know........