30A power outlets are not gfci, only 20A and less. Thats not it.
Breaker tripping in ped. , replaced with new by camp, still tripped., but not in camper main panel. Thats amperage overload that could be caused by poor connections or undersized wiring downstream of the breaker. Assuming your cable to the rig is a 10/2 in good condition then it may be poor connections in the ped between the breaker and outlet, or in your rig where your shore cable connects into your panel or junction box.
Poor connections will heat, which causes resistance, resulting in low voltage. As the result, amperage increases to supply the wattage demand. Its why welding cables are so big.
Several times we have had connections on our side overheat, its age and corrosion due to weather in outdoor environment. We fix it right away, its not something that can be a preventative maintenance issue. Inspection yesterday, cannot see a problem tomorrow. Its like a car, it ran fine this morning, broken down now.
. A few times we have found a heated weak connection in someones camper. Inspect your connections ,cable , junctions, then have the camp inspect and verify adequate sizing, sound connections.
Knowledge of wattage of your load to keep you below the threshold of your available amperage would help you convince others that the problem is not yours. And add to your safety.