2008 3023 Water Heater Question

Hello- I recently red the manual for my 2008 3023 Trailmanor and I need some help in confirming how the water heater works.

I understand that I have the 6 gallon model that runs both on Electric and Gas. The questions I have are:

1. If I am running on Electricity (using the "On" switch OUTSIDE the trailer), do I need to use the "On" switch inside the trailer using the red button as well or is that only used for Gas?

2. When I am finished with the hot water, do I need to turn off both "On" buttons or can I leave them on during the trip? I had heard you can burn up the water heater by leaving them on but I am not sure if that is true.

Thank you very much for the help!

Joe