You'll have to make a pigtail that will allow you to plug both into the same socket or add a socket for the boat plug. I've also seen some factory made for sale.
The following link has one you could add to your truck harness to adapt the boat wiring. It's for an older model but you can get them for most any truck.
http://www.google.com/aclk?sa=l&ai=C7ZnF_2x1U6i6BcWksAeW1ICYAe7aq8YEvrGzoIsBhta694sCCAQQBCgFULe83m1gyYa0hrij0BWgAdzDif8DyAEHqgQlT9DtsS2R6hEx6ypM5LEsVamhwFqsHhYMc8NrE7f8nZ2tEMaRGMAFBaAGJoAHjLx2kAcB4BK8styt1Zz4ioYB&sig=AOD64_0nyts0Nh4P4bmu6eRy4b3jir9IYQ&ctype=5&rct=j&q=&ved=0CDkQwg8&adurl=http://www.carid.com/1973-gmc-ck-trailer-hitches/draw-tite-t-one-connector-4171872.html
