Just to be sure i think everyone is talking about the camp ground PEDESTAL Breaker not the Trailer Breaker..
I turn off the pedestal breaker - check the receptacle - plug in shore power cable - then turn on circuit breaker.
I used to check the service alot with my meter for proper wiring but have got lax on the of late. I am only using the 30AMP receptacle with my setup.
I do inspect the receptacle for signs of wear and black burn marks. If it looks bad I will use the 50AMP receptacle with ADAPTER.
I certainly don't want my 30AMP Shore Power Cable plug to end up looking like this or worse due to poor connections and overheating.
Roy Ken