Originally Posted by TonyD
My first guess would be a failed electrical heater element.
However, if that is ruled out then consider the following excerpt that says it better than I can: Why is My RV Shocking Me?
These electrical shocks can be caused by a reversed polarity problem in the electric receptacle that your RV is plugged into, a polarity problem in the extension cord you are using to plug in your RV or to a shorted wire somewhere in your RV's electrical system. This problem can also be caused by an improper ground in the receptacle, extension cord or in the RV.
..... reversed polarity which is the most common cause of "Hot Skin" in RV's.
Now we need to determine which part of the electrical system is causing your problem. You can use your polarity tester to help determine the cause.
First, Unplug your RV from Shore Power and then plug the tester into the receptacle that the RV was plugged into. To do this test you may need a 30 amp male to 15 amp female electric adapter so that you can plug the adapter into the 30 Amp plug. You may find that the tester will indicate that the polarity of the receptacle is reversed. To solve this problem the electrical outlet needs be rewired properly or you will have to plug into a known good receptacle.
If the outlet shows no problems then we know that is not causing the shocks. If you are using an extension cord to plug in your RV we need to check that next. Plug the extension cord into a known good outlet and plug the tester into the extension cord. If it indicates that there is a problem with the extension cord then the extension cord needs to be disposed of.
Sorry, but the above information is incorrect.
First - Reversed outlet polarity (Swapped Hot and Neutral) will NOT cause a hot skin condition if the ground wire (EGC) is intact and correctly bonded all the way back to the incoming service panel from the power company. That's an old wives tale that I'm still beating to the ground.
Secondly, none of the 3-light polarity testers will find a really dangerous mis-wiring problem I've name an RPBG (Reverse Polarity Bootleg Ground). Please read this link where I introduce the idea to the RV industry. The RV Doctor: Friends of Gary - Mike
Thirdly, an electric hot-water heater element with a broken hermetic seal will leak current (around 1 or 2 amps) to the chassis of the RV. But if the RV is properly bonded/ground back to the service, then it's impossible for any significant voltage to exist as a hot skin. Maybe 1 or 2 volts, but certainly not the 40 volt threshold where it gets dangerous.
Fourthly, a loose, missing. or broken ground wire (The EGC or Equipment Grounding Conductor) by itself may no cause a voltage to be noticed when touching the skin of the RV. But virtually EVERYTHING leaks a little current to its chassis when plugged into an outlet. And it's allowed to leak these small (under 1mA) currents and still be UL listed and NEC compliant. But all these little leakages from your various appliances are additive, so you may not feel a shock if not much is turned on inside your RV. But even a single MOV power strip can leak enough current (1.5 mA) that you can feel it. Again, if you have a proper ground wire on your shore cord connected to a properly ground-bonded receptacle, then it's impossible to develop a hot skin voltage. The circuit breakers will trip first.
Finally, it's a bad idea to stand in the water and flip any switches connected to electrical power. That's because even if your RV chassis is properly ground-bonded, you still can have conductivity via any water on the switch itself.
I think that the quickest and best way to test for an RV hot-skin condition is still a NCVT such as a Klein NCVT-1 or Fluke VoltAlert. You just need the standard 40 to 1,000 volt versions, not the 24-volt versions. See