My coach is a 2001 Horizon, and has a gch10A-4E heater. If yours is a similar installation and heater, this might help. Don't know for sure because I don't know your coach, so it may not be the same.
I just had to do this myself. It most likely will be necessary to pull the water heater. It's really not too bad of a job. You will first need to make sure power is off to the unit, and the propane is turned off at the tank. Remove the drain plug, and flip open the pressure relief valve to facilitate draining. Remove the door of the water heater by removing a couple of screws at the hinge, then slide the door off. Disconnect the propane line coming in on the left. Should be a 3/4" wrench. At this time, remove the 16 screws around the face of the water heater. Using a putty knife or a wide screwdriver, pry the edge away from the body. They used a butyl rubber caulking around it, and it's kind of a pain to get off. Once you've gotten this off, you can start to pull the water heater out. If you have a milk crate handy, use it to rest the water heater on (or something of similar height) when you pull it out. Carefully slide the unit out. If you have the motoraid option, you might have to reach behind the compartment and feed the heater hoses in a little to help with sliding the tank out of the compartment. Once you get the heater out far enough to reach the back, you will need to take off the cover on the back. It is about 4" x 6", and held on lightly with a couple of 7/16" nuts. Once it is out of the way, you should be able to see the element. There are two phillips head screws hold the wires on the element. You only have to loosen these to get the wires off. Using a 12" crescent, unscrew the element. Just do things in reverse to put everything back together. Make sure the new element has the o-ring on it before putting it in, and make sure you screw it in by hand as far as you can before putting a wrench on it, as the tank is aluminum, and if you cross thread it, you're looking at a new tank. Also, make sure you use the metal part of the element, not the plastic part the wires hook to. I used a plumbers tape to seal the heater back to the compartment instead of the butyl rubber.
2001 Itasca Horizon