I can run my 13k BTU AC plus the water heater successfully. If I leave the trailer with the cats in residence, I turn off the water heater so that only the AC is running.
I originally popped breakers in super-hot weather until I ventilated the upper cabinet where the breaker box is installed. The heat from the breaker box plus the sun on the skin was driving the temperature to the point where I couldn't keep my hand on the metal breaker box. It stays nice and cool now that I drilled a row of vents into the cabinet top behind the front face. When it is really hot, I leave the cabinet open to get even more airflow.
John W. Irwin
2005 Classic 28 "Sabre-Dog III"
2013 Silverado 2500HD Duramax/Allison LTZ
WBCCI #9632, TAC TX-10