I know this is an old thread but mine had been doing that since we got it, touch the frame, bumper, step or anything, even the dog got a shock sniffing the step.
So I got bored to today and went and put a meter on the frame and sure enough had about 9 volts running through it so I tested it by plugging in the generator and it didn't do it, it was only when plugged in to shore power. All I did was take off the electric box cover where the power goes into the MH and tighten all the big wire nuts and tested it again and everything is fine. I'm so lazy it only took me 10 years. :D