If it's a steel plug with a long magnesium (looks like aluminum) anode rod, you have a Suburban water heater. With obstructions around the hole the anode goes into, it's very hard to install one with just the strength of your fingers. I use a socket with an extension bar. I wrap the threads with teflon tape then the head of the anode with electrical tape so it presses hard into the socket. Then I work it till the anode and the extension are lined up. That way, it's easy to know how the anode's lined up inside the tank, with how the extension looks on the outside.
With tape on the threads, the anode doesn't have to be all that tight. My guess is that if you can get the anode installed, and the bypass valves in the correct position, you will have "fixed" the appliance. If it wasn't "leaking" last season it probably doesn't have an actual leak. Just the Anode out, which is decent winterizing. Some remove it to drain the heater then put it back right away. Others leave it out for the winter.
Speak to other campers, or campground maintenance people. They might be able to help you or loan you a tool to install that element.