[JRTJH]

I'd replace the 30 amp breaker. It's nearly 17 or 18 years old, has "carried a lot of amps in its lifetime" and deserves to be retired.... My guess is that you're pulling very near 30 amps through the A/C, microwave, converter, 12VDC circuits in the refrigerator and any TV, lights, etc that may be on. So, if the current circuit breaker is "just a little weak" and trips with 28 amps (due to past use, wear and weak springs) that would explain why it's always the "inside circuit breaker" and not the "pole circuit breaker"....

Replace it and try to limit concurrent A/C and microwave use. Turn the A/C to "fan" to use the microwave, then back to "cool" once the microwaving is done....

Additionally, you might consider adding a 15 amp "auxiliary power line" to the trailer. You can buy a "power inlet" that mounts in a 1.5" hole and looks similar to the detachable 30 amp shore power inlets. Install it near the kitchen, then route the ROMEX up through the cabinets to the microwave area and plug the microwave into the "auxiliary power source" so it isn't drawing from the trailer's 30 amp supply....