Operating water heater with gas vs. electric

Hello Trail Manor friends. We own a 2009 2720SL 25th Anniversary
edition. I am having some difficulty with the water heater. It is self-igniting, so it states not to light the pilot light, it will do so automatically. It heats exceptionally well using electricity, but I can't operate it with propane gas. I have followed the instructions in the manor. "To operate by gas, turn off all electrical power to water heater at switch under sink. Turn off gas supply (DOES THIS MEAN THE GAS SUPPLY FROM THE PROPANE TANKS TO THE CAMPER?), because I can see no other gas valve specifically to the water htr.? Wait 5 minutes, Turn on gas supply. Turn on electric power to the water heater(THE SWITCH UNDER THE SINK?) Turn switch to on position (DOES THIS REFER TO SWITCH INSIDE THE WATER HEATER PANEL?) THE ONLY STEP THAT i SKIPPED WAS TURNING THE GAS OFF TO THE WATER HEATER. So, what do you folks thin I am doing wrong?