I recently fount out my solution to the same problem, but I was connected to shore power. First, AC voltage measured 108, not the nominal 120 Volts. Second, I had the water heater on electric, not gas. Main breaker is 30 Amps. AC breaker is 20 Amps, while water heater is 15 amps. Add to that the low voltage and 100+ temp outside leads to a tripped main breaker.
2005 Newmar DSDP 4024, Tow vehicle 2008 Jeep Liberty, Demco Dominator tow bar and base plate, US Gear Brake Controller.
Member of FMCA, Newmar Kountry Club, Good Sam, IRV2.