Since you have the Atwood brand name heater, you might start with the owners manual from our library.
Forest River Forums - Downloads - Water Heater - Atwood Water Heaters
Pagr 4 tells about the electric heating element and that there is a switch on the BACK
of the heater, as well as a resettable hi-limit switch you can press with a pencil or non-metallic object to try. It has a pic of the location.
You said the dealer winterized it for you. Did you manually verify there was water inside the heater before turning it on by electric, by opening the pressure valve on the front of the heater.
If not, then there may have not been water in the heater, and the element is burnt up.
However you stated it was working on gas, so I am assuming you are getting hot water, thus the bypass valves have been set for summer use, and are not still in winter mode (thus the water bypassing the heater).
If the bypass valve is still in winter mode, you cannot verify there is water in the heater just by turning on the hot water taps inside your trailer........................... since the purpose of the valve(s) is to bypass the heater, thus the cold water line is now merged into the hot water line................so you will always get water from the hot water tap, it'll just be from the cold water line.