Similar thing happened to me and it was a bad ground with the extension cord I had plugged between my house and trailer.
There is more to this than just the hot wire rubbing thru and making contact with trailer metal. There should have been a path for that hot current to return thru the ground system. That should have thrown the shore power breaker or the generator output protector. Perhaps the outlet you are plugging into for shore power has an open ground, or perhaps is mis-wired. Or, they may have compromised your ground system and opened the ground path from trailer to shore power / generator by mis-installing the transfer switch. Or, your shore power cord may be mis-wired or have an open ground. Please use that NCVT to make sure you don't have hot skin when you get the trailer back. I would also use a test meter to make sure your shore power ground line is good.
Update. Picked up my Cyclone on Tue. The condition was indeed caused when the transfer switch was replaced. The tech said that the person failed to secure the wiring on the shore power side, and it wore through the sheath. He was reading 120V on the skin. Not good, and considering we were standing in water when it was 1st discovered, even worse.
When I picked it up, it was connected to shore power, and I brought along my NCVT. In addition, the tech had good ground wire coming from the panel in their shop, and a voltage meter. No voltage, everything was good. I'm still not happy about the 4+ week wait, not to mention their failure to get the necessary parts for some minor issues, within that time frame. I will have to return it later or do the work myself. Thankfully, I didn't have anything major scheduled during that time.
The guy who was the source of the problem was a do-it-yourself person who installed his own AC incorrectly. He also had some bizarre hydro line running from his trailer to his shed. He put male plugin.