Although I totally agree with the three prong cord with the grounding connector, I am at a loss how the trailer had a floating voltage in the first place. In order for this to happen the ungrounded conductor would need to make contact with some metal of the trailer in order to conduct current to the metal panel. Unless I am missing something the addition of a safety grounding conductor would merely mask the original problem. It may save his life in wet weather but not fix the original problem. If the grounded conductor (white wire) is also attached to the frame and the two prong plug is not polarized (and reversed in the outlet)this could give a floating voltage to the trailer and the three prong plug will correct this. If the house outlet is reversed and the grounded conductor is attached to the frame it would give the same results. Is the grounded (white wire) attached to trailer frames? Please correct me if I am missing some detail.