Make sure your shower miser handle is in the right position. If it is turning white from blue then the hot water is going back to the fresh water tank. What model do you have? Also refer to your documents on the water heater about operation in electric and gas mode.
Remove the panels from the pass-through storage compartment to get to the area under the bed. You can get to the backside of the hot water heater there. Make sure the bypass valve is closed, and the cold and hot water supply valves are open. If the trailer was winterized, it is likely the bypass valve is open and the cold/hot water valves are closed.
Is the trailer plugged in to electrical service? Are the propane bottles valves open? Are the switches for gas/electric hot water heater turned on as appropriate? (When I want quick hot water, I use both at the same time.)
Open the outside panel for the hot water heater, and press both the reset buttons at the same time there.
Until the OP comes back and provides more information, we're all guessing.
Dan-Retired California Firefighter/EMT
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package