I believe our 235 works like this:
There is a switch outside in the water heater panel that when turned on, will set the unit to electric. It's automatic from there, if you have AC power then you have thermostat controlled hot water.
There is also a control panel inside the camper next to the sink. If you have your gas connected and you turn it on, a red panel light will show that the gas burner is on and you will now be on gas hot water.
When winterizing, you turn the electic to off and the gas to off.
I like to camp with gas hot water turned on because gas heats the water quicker and in the evening, we use alot of hot water.