As chrisbailey13 noted, there are two furnaces. The image he posted is one of two look-alike furnace vents. One is at the left rear of the coach and the other is on the right side just aft of the entry door and outside monitor. Since there now appear to be two owners who believe there is more than one water heater, could anyone post a photo. (We seem to all agree there is one at the right rear of the coach, but if there is another, please provide photo.) I have a 2015 364TS and for the life of me can't find a second water heater. But, as my DW can attest, I've been wrong a whole bunch of times!
2015 GT 364TSF