GFCI Intermittent trip issue

We have a 2013 176t. I am trying to diagnose an intermittent issue with the GFCI. The problem is that it trips periodically. I'll make a long story short, but hopefully not leave out important details. I think I am dealing with a lot of red-herrings and coincidences that are throwing me off from diagnosing the issue.

The GFCI has only ever tripped while "camping" at Disney (ft wilderness). 

The first time it happened, we were plugged into the 30amp with the AC blowing (Florida...) and the fridge on ac, and lights on the exterior plug. I reset it, good for a short time, then tripped again. I unplugged the fridge then reset the GFCI and it was fine for two days (before going home). I dropped the Rpod at lazydays dealer on the way home. They tried to figure out the problem, decided to replace the board in the fridge, and we hoped everything would be good.

This weekend we were once again at Disney in a full campground (always proud to be the smallest camper in a sea of monster RVs). The GFCI tripped again with no ac running but with the fridge running and lights connected to the exterior outlet. I unplugged the fridge, and could not reset the GFCI. Unplugged everything from the outside outlet and still could not reset the GFCI. Tried several time. Also tried unplugging the 30amp, still no luck. 

Now it gets weird or red-herring territory - the next day, after many of the monster RVs moved out around us, the GFCI could be reset and stayed that way for a day before we left.

So, what do you think the problem is here:

1. Problem with the power in the campground (remember this is Disney).

2. Problem with the GFCI - are there actually good and bad GFCIs?

3. Could it be a problem with one of the outlets attached to the GFCI - maybe the exterior outlet was damp the first day and then dried out after that?

4. Other thoughts?

This is perplexing, so any advice is appreciated.

Cheers

fred

Second, order the NCVT that fwunder linked to.  Also buy a plug-in outlet tester (that has the 3 lights).  The later will cost about $10.  Then see the link in my signature.  The first item in the list that pops up will explain how to use the NCVT and plug-in tester.  USE THEM EVERY SINGLE TIME YOU PLUG IN - anywhere, even at home.  I almost killed my kids before I started doing this.

My hypothesis is not low voltage, but either a problem with the wiring at Disney, OR a problem with wiring of one of the other RVs at Disney.  Yes, a wiring problem with another RV can cause problems with your RV.  The other possibility is normal current leakage from things you have plugged into the GFCI circuit.  If your phone charger is leaking 3 ma (normal), and your laptop power supply is leaking 2 ma (normal), then you are just at the 5 ma trip limit and anything else that leaks a bit will cause it to trip.

Camping at the Disney Ft Wilderness is an interesting experience - our little rpod with spacious rdome is surrounded by massive trailers and RVs with people watching 42" or larger flat screens outside. Sometimes it can be surreal...