For marinade, in a small bowl, combine pineapple juice, cooking oil, molasses, lime juice, brown sugar, mustard, soy sauce, and seasoned salt.
Place roast in a plastic bag in a bowl. Pour marinade over meat. Close bag. Marinate in refrigerator for at least 2 hours or up to 24 hours, turning bag once or twice.
In a covered grill, arrange medium coals around outside edges. Test for medium-low** heat above center of grill (not directly over coals). Lift meat from marinade; discard marinade. Place meat on rack in a disposable foil roasting pan. Place pan on grill rack, but not over coals. Close grill hood; grill 2 to 2-1/2 hours or until a meat thermometer registers 165 degree F (temperature will rise 5 degrees F after it's removed from the grill). Add more coals as necessary to maintain heat.
Transfer meat to a warm carving platter. Cover with foil and let stand for 15 minutes before carving. Makes 18 to 20 servings.
Tie up roast with string, if the butcher didn't do it for you.
To test for medium-low heat, you should be able to hold your hand over the drip pan at food height for 5 seconds before you have to pull away.