Always nice to have the adapter on hand to use. Most everyone uses the 30AMPS receptacles and alot of them don't look very good connection wise...
The 50AMP Receptacle next to is usually as clean as can be...
I got mine from WALMART... Looks like this...

This is a diagram showing how it works... Notice that it only taps into one HOT side of the 50AMP Service for you to use... Although you have 50AMP service available to use your trailer 30AMP breaker will keep you from using more than than 30AMPs otherwise the trailer 30AMP breaker will trip.

Roy Ken