I should have added to "no cct breaker action" was due to no ground .
What we don't know is, were the other RVs plugged into a same pedestal or was this problem spread out through the camp ground.
Since it's generally one RV per campsite, and one Pedestal/Outlet per campsite, it's safe to assume these four RVs were spread across four campsites on four different pedestals. All the pedestals in a campground section are generally daisy-chained together.
The original fault would be a wiring defect that brought hot side of AC to chassis of the RV. Hard to say where that happened.
Yes, that's most likely the cause. I've seen shorts like this created with wiring laying across sharp metal struts in the chassis of the RV, or wiring that's been pinched between the floor and a metal support beam, or even by a screw drilled into the wall which pierces a wire run. That's a low-impedance/high-current fault which will have full circuit breaker amperage available for the fault current.
An example of a mid-impedance/mid-current fault would be an electric hot water heater with a leak in the heater element. That will provide about 1 to 2 amps of current to the chassis.
A high-impedance/low-current fault would be an appliance with a leaky transformer plugged into an interior outlet in the RV. Leakage can be anywhere from a few mA up to a few hundred mA. Some will trip a GFCI, while others won't.
Everything plugged into an outlet exhibits SOME leakage to their chassis. For instance, a Crown iTech amp will leak up to 3 mA and still pass final testing. A common Surge-Strip will leak 1 to 2 mA. A double-insulated piece of gear will have to have less than 1 mA leakage (IIRC less than 0.7 mA) to pass UL listing.
But this all begs the question. How does ONE RV with a wiring problem that creates a line-to-chassis fault-current affect several OTHER RVs in the same wiring loop. And how do they all get a "hot-skin" voltage?
Hint: I call this a "Reflected Hot-Skin Voltage".