The 115VAC black wire is "HOT".
The 115VAC white wire is "NEUTRAL".
The 115VAC green or bare copper wire is "GROUND".
The 12VDC (usually white or red) wire is "HOT".
The 12VDC (usually black) wire is "NEUTRAL" and "GROUND". (12VDC color
codes are not standardized or reliable.)
The 115VAC white wire and green/bare wires should not be connected
together anywhere before the land (shore) main power panel's
neutral/ground bus. Of course we have no control over the park wiring.
The 115VAC panel's neutral bus in the trailer should not be grounded to
the trailer frame or body (metal). It is not reliable as a true ground.
The potentially main source of trouble is in the RV park's wiring, which,
especially if outside city limits and the reach of a city electrical code
department, may have been wired by an amateur, or have been repaired or
modified by an amateur who didn't know what he was doing. If the polarity
is reversed, the "HOT" of the land power would be connected to the
frame/body of the trailer and the "NEUTRAL" and "GROUND" of the land
power would be connected to the "HOT" (black) wire of the trailer wiring.
That is what the green and red lights on the voltmeter box that is on
many RVs is supposed to detect.
Not only would this make the step and body of the trailer have 115 volts
relative to the ground (dirt the trailer is parked on), it would connect
the 115 volts to the 12VDC "GROUND/NEUTRAL" wire in the trailer, which is
supposed to be grounded to the frame/shell. Not good.
So the RV electrical code was revised to isolate the 115VAC wiring
completely from the trailer body/frame.
The trailer body/frame should have its own separate ground strap with a
big alligator clip on it, clamped to the land power pedestal, conduit (if
metal) or some other known good ground, like the water spigot IF it is
iron (galvanized) or copper, NOT plastic.
The only time it's "legit" to have the "GROUND" and "NEUTRAL" wires
connected is at the land power main panel's neutral bus bar, which is
SUPPOSED to be properly grounded.
Also, in old houses that have only 2-wire wiring with no ground wire
(like "12/2 with ground") sometimes the ground receptacle, the round
opening in a replacement 3-prong outlet, is strapped with a little piece
of bare wire to the "NEUTRAL" screw of the receptacle when the old
2-prong receptacles have been replaced with 3-prong receptacles. This is
better than leaving the ground receptacle unconnected to anything and
giving the impression that it is good just because it's there. The proper
thing to do is rewire the house wiring with 2-conductor plus ground
romex.
Al