Why in the world do you have a 50 GFCI for your RV hookup.
The only place that would be required is a spa or hot tube.
More than likely you have a problem in the rig but GFCI do go bad but not often. I'd check with a good VOM (volt ohm meter) for a continuity between the ground and neutral in the rig. Of course with the power off !!!!!!
You should get no reading at all.
If you do something is amiss in the rig.
Other way is to turn off every circuit breaker in rig, turn on one by one and figure out which circuit is causing the problem and go from three.