Rv Atwood and surburban waterheaters have fixed thermostat
When I had an Atwood w/h I installed an adjustable thermostat and turned it up to the highest setting but to prevent getting burned I installed a automatic thermostatic mixing valve on the back of the water heater that mixes in cold water to get 9 gallons of hot water out of a 6 gallon water heater
If the temperature out of the water heater is to hot add the thermostatic mixing valve which it has an adjustment to control temperature
Now I have a surburban water heater because my Atwood died
It had 130 fixed thermostat I replaced with a 160 degree fixed thermostat and still using the thermostatic mixing valve
High limit thermostat is fixed at 170 degrees and the t&p valve is fixed at 210 degrees which I kept for safety