Preheat grill to around 400 degrees F or medium-high.
Spray a large sheet of tin foil (double it up if you aren't using heavy duty foil) with non stick spray. Place potatoes in center of foil and lift the edges slightly (so that the butter doesn't run out)
Stir together melted butter, garlic powder, Italian seasoning, seasoning salt and pepper. Pour over potatoes and stir gently.
Seal foil around potatoes as much as possible. Place on the grill on direct heat, and cook for 20-25 minutes, until tender, stirring once or twice.