Starting at the supply outlet and checking the polarity is #1. Then check your umbilical cord. With an Ohm meter, do a continuity test on each wire in the cord. Then try cross-testing them. If you get any reading other than zero when you cross test, throw the cord away and get a new one as it has been compromised and you are getting a shorted power supply which will case your hot skin problem.
If your cord is OK, check inside the junction box of the trailer to see if everything is properly wired for polarity.
A hot skin basically is sending the hot leg of the 120VAC thru the trailer ground or neutral and when you touch the trailer, YOU are completing a path to ground that allows the current to pass thru you, causing the shocking experience.
Check back and let us know what you'[ve found!
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