Tear off two squares of aluminum foil large enough to fold over 3 ears of corn. Place 3 ears of corn in the center of each foil square. Divide the butter, garlic salt and seafood seasoning between squares. Fold up the foil into packets and seal well.
Place the packets on the grill and cook for 15 minutes, flipping halfway through.
Remove the packets from the grill, open carefully, and sprinkle the corn with the Parmesan.