Badge165: I too have a 2012 3700RL. To access the back of the water heater, remove the back wall of the pass through compartment on the passenger's side. It has like 4 or 6 screws holding it in place. You may want to disconnect the electrical outlet and 12V and cable TV box so you can totally remove the panel.
I had a problem with mine a year ago and posted the pictures of getting access. Go to Thread
https://www.montanaowners.com/forums...ad.php?t=86637 and locate Post #21. If you have any question, ask away.