Looking at a pic of your TT and the floor plan, it appears your water heater is under the rear bunks. Remove the mattress from the bottom bunk and you can probably lift up the plywood and access the back of the water heater.
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2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado 1500 Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10