Any time you receive a shock from the frame of a trailer, you have 2 problems or faults. The first is leakage (a "fault") to the frame. This could be a loose or broken wire, a failed water heater or refrigerator
element, failed converter or other appliance, or improperly added wiring.
The second problem is a faulty ground system. If the trailer grounding system is correct & the trailer is plugged into a correctly wired receptacle, a fault to ground capable of carrying high current will trip the source circuit breaker or fuse. If fault to ground has enough resistance that it limits the current to under the rating of the circuit breaker, a good ground will carry most of the fault current, preventing a shock. This is why it is important to have a continuous low resistance ground connection.
Both problems need to be addressed. If you solve the open ground problem, don't stop there. While the shock goes away, sooner or later you are going to end up in an "open ground" situation where the shock hazard shows up again. Another problem with a ground fault is most GFCIs will trip - you may find yourself in a location where the only receptacle is a GFCI. I've run into two US campgrounds (both in Missouri) that had GFCI 30 amp receptacles!
Find the source for the fault to the frame & fix it. Shutting off the trailer breakers one at a time, unplugging or disconnecting appliances, etc will help identify where the problem is located. Again, typical ground faults are caused by bad electrical
heater elements, older transformer type converters, and broken, loose or damaged insulation 120V wiring.