I might add that they are often at or near the rear of the water heater, which is ~ 1.5 feet deep. Locate the heater on the outside of your unit and then figure out what panel you have to remove to access the back end of the heater. Note that the panel may be on the side of the water heater and not necessarily behind it.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.