Did you figure this out? I have not pulled the pass-through wall. That was the only thing I could find as a possible way to access the heater. Not sure if there will be bypass on the tank once I get to it.
2015 A122S and 2011 Work and Play WR30
2005 F-150 SuperCrew, 5.4L, tow package, 3.73 axle
2011 F-350 SuperCrew, 6.7L, FX4, 4x4, DRW, tow package, 3.55 axle