New to you... It is possible the water heater was bypassed for winterizing last fall. Like others have said, open the pressure relief valve, it's outside behind the water heater cover. If no water comes out, you have no water going in. If that's the case you will have to find the back side of the water heater inside the trailer. Might be behind a piece of paneling being held in by a couple screws, in a cabinet or even under the bed. Once you find it it will be fairly obvious what you need to do to get the water going into the tank. If not google RV water heater bypass for diagrams. Oh, and if it is bypassed and you turned on the electric element, your going to need to replace that once you get the water issue figured out.