I have an Atwood 6 gallon heater. There is a thermostat but it is not adjustable and must be preset at close to boiling. Actually I believe I read the temperature is set at about 180 degrees. That is way too hot as far as I am concerned. I suppose I could look for an adjustable thermostat but instead I just time the heating. I have a cheap timer that I velcrod on to the kitchen stove vent. If I have recently filled the tank with cold water, the water heater needs to run about 20 minutes. For water that is a room temp, I need about 16 minutes. I try to heat the water so I get a hot comfortable shower without using any cold water. Since I only use about 1 gallon for a shower and my tank holds 6, the temperature remains pretty constant for the whole shower. My wife uses about 2 gallons and I turn the heater to back on while she runs the shower and again the water temperature stays pretty constant.
I don't bother with hot water for washing dishes. I have a plastic basin that I partially fill with warm water heated on the stove. That helps keep the water use down and it only takes a minute or two to heat the roughly 1 quart of water I need. Endless running hot water is great at home but just not worth it when living in an RV. That is partly a compromise I make since I rarely stay in places with hook ups.