Often, in fact usually, in our coach we have the same problem. I have checked everywhere and cannot find any incorrect or poor wiring or connections. Someone told me that some GFI circuits don't "Play Well" together.
At home, and at a nieces place, to use a GFI protected outlet we have to kill two breakers in the coach, plug in the shore power then turn the coach breakers back on. I discovered this when trying to trouble shoot a suspected faulty circuit in the rig:
I turned off all breakers in the coach then plugged in the shore power. Shore power GFI didn't trip.
I then turned on all other breakers one by one waiting for one to trip the GFI at the post. Nothing triped it, all circuits in the coach worked, including the GFIs in the rig. (head and galley)
I then unplugged the rig and pluged it in again: Breaker tripped.
Seveal rounds of this found 2 15A breakers that had to be off when plugging in to the GFI outlet. The breakers could then be turned on without tripping the GFI.
When I later related this to an electrician brother-in-law his first comment was GFI breakers in the coach were causing it. He said it frequently happens.
I would strongly suggest that you FIRST have all the circuits in the coach checked by an electrician. If they find no fault then the only course is to do what we do.