Fourfourto,
I recomend the 7 pin round RV type plug. It is a very versatile plug , and if you ever need to tow a trailer with the 4 pin flat type plug, there is an adapter that just plugs right into the socket on the truck.

I adapted the Army trailer I showed in the past to accept the 7 pin round plug and it makes towing a great deal easier to connect and dis-connect.
Get some pics out when it is complete.