Before buying and installing a new water heater, try some trouble shooting.
>Disconnect fresh water supply(or turn off at source)
> Locate drain valve on heater and drain. If no drain valve locate anode Rod and remove it- drain water heater tank. You may need to open a hot water faucet to help facilitate. Then refill (close valve/replace anode Rod).
> another area to check, locate bypass valves, you should find an access panel or opening inside the trailer on the back side of water heater, verify the valves are completely open and shut in the proper mode (YouTube is your friend, many videos of water valve bypass for wintering can be found.
If you water heater is heating I donít think itís a heater issue, the water lines could just need to be ran to flush out trapped air.
Hope this helps. Good luck and no doubt someone else may chime in with better info.