1) GFCI source you are plugged into, whether a GFCI outlet, or on a master GFCI breaker, may not play well with your RV with it's own GFCI circuits
2) Your RV has other appliances or devices 'ON' and drawing power, even if they are the 'silent' type, such as the battery charger/converter and the Electric water heater element.
3) The shore power's source/circuit also has OTHER appliances or devices drawing power at the same time you are, overloading the circuit.
separately, there is a difference between 'tripping', which is really what happens when a BREAKER trips, from overloading, and the GFCI 'tripping' due to moisture, or even, like may be in your case, two GFCI circuits not playing well together.
two Campers, two Electric cars
former diesel pusher traveler