Used to happen to me also with a 30amp TT. I just got into the habit of turning off the AC whenever I started the microwave. I can't remember which breaker tripped, I just figured I would make sure it never happened again...and it didn't as long as the AC was temporarily switched off.
We have a Shasta Oasis 26RL and have run the AC and microwave at the same time and the only time I have had the breaker go was when it was parked in our driveway while getting ready for a trip. I had it plugged into an outside outlet on the garage. My wife wanted to warm up her coffee and as soon as the microwave started the breaker went but not in the TT it was the garage breaker. We have not encountered that while travelling.