Are you saying the neutral (white) wire is connected to one of the hot leg terminals, with the hot (red) wire hooked to the neutral terminal? Is the fourth ground terminal connected properly? If that's the case, then yes, he will have a serious problem if he plugs into it. Donn is mistaken though, in that there is no difference in the way RV 50 amp 4-wire outlets and residential 50 amp 4-wire outlets are wired. The outlets are identical, and both should measure 220VAC between the two hot terminals, and 120VAC from each hot terminal to the neutral terminal. There should be zero volts between the neutral and safety ground.