Welcome to the forum.
Are you getting warm water or no water flow at all. Thinks to check.
If you are you getting no water flow at all on the hot water side at all the faucets it's probably this.
The check valve on the output line (top Pipe) has failed which is quite common. You'll need to gain access to the backside of the heater. Remove the top pipe then remove the fitting which is screwed into the tank. As a temporary fix, using a screwdriver, knock out the internals, then screw it back in with pipe dope. If you'll never need to winterize the RV, you can leave it that way. These valves are available at Home Depot.
If you are getting water but it's not hot, make sure the water valves at the shower are turned off and not just at the spray wand. Also check the outside shower if you have one.
If you are getting water but it's cold, it's may be because your bypass valves are not positioned correctly.