No need to worry, nothing is wrong.
A microwave is a fairly inductive load, so is an air conditioner, and when the voltage sags slightly at the campground, the amperage demand increases.
microwave - maybe 13 amps
Air conditioner - 14 amps, low voltage maybe 16 amps
converter running at all times - maybe 1 - 6 amps
they add up to around 30 amps, and that is a conservative estimate. The main breaker will go because is is seeing more than 30 amps, the microwave breaker will not, since it is not seeing more than 15 amps.
Nothing wrong with your trailer, you are just at the edge of the capacity for a 30 amp service.