At the dealer, are they testing the water temp by opening a valve on the water heater itself, or the trailers sink/shower taps?
The reason I ask, is if you have the water heater bypass valve incorrectly set, or maybe have the inside/outside showers turned on, but are closed at the shower head themselves...............it will allow cold water to mix in with the hot water, thus lowering the temp............when you check it at the faucet.
However, the water inside the water heater is hot, and if checked by opening the pressure relief valve on the water heater itself, hot water is what will come out there.
Just trying to make sure you and the dealer are on the same page, and testing from the same spot.
2011 Flagstaff 831 RLBSS
I've just ordered a chicken and an egg from Amazon.... I will keep you posted.