50 amp 220 volt concession trailer service question

Hello, my name is Mike Riordan, owner of Riordan & Sons Electrical Services. I have been asked to provide a 50 amp 220 volt 4 wire circuit and receptacle for a concession trailer,  for an annual fundraiser festival that benefits a local hospital and library. My question is, is there a standard configuration for a 50 amp 220 volt shoreline? If anyone could provide a Nema # , photo, and/or good description of the shoreline plug, that would be all i need. Thanks in advance, your time is appreciated. 
Mike Riordan 
Riordan & Sons Electrical Services 

It may be similar to a 50 amp RV (recreational vehicle) service used by motorhomes. Google "50 amp RV service" and you will find the standard plugs and outlet boxes often used for RV parks.
 
I had a 30 amp services installed at my garage for my camper van and my electrician also did not have a clue about what outlet box to install until I suggested he check with the RV dealers and Camping World rather than his usual electrical supply houses.

Thank you for your reply! I will check that out.