Was plugged into shore power via a Wally World cheapo extension.
Ran the ac for a few minutes then the shore power breakers tripped.
The connection must have been loos or got moisture inside it, and there was arcing inside the receptacle hot enough that the pin in the trailer side plug melted through some internal insulation resulting in a hard short to ground.
Was able to repair the plug, and replaced the receptacle with a proper weatherproof receptacle, UL rated, from my old company, Eaton. This is a little extra bumps to carry around, but it will keep the electrical connection dry and secure.
Be wary of the cheapo extension cords!