In a small bowl, mix brown sugar and seasonings, sprinkle over ribs. Refrigerate, covered, at least 1 hour.
For sauce, in a large saucepan, heat oil over medium heat. Add onion; cook and stir until tender, 5-6 minutes. Stir in remaining ingredients; bring to a boil, stirring occasionally. Remove from heat.
Wrap ribs in a large piece of heavy-duty foil; seal the edges of the foil. Grill, covered, over indirect medium heat until ribs are tender, 1-1/4 to 1-3/4 hours.
Carefully remove ribs from the foil. Place ribs over direct medium heat; baste with some of the sauce. Grill, covered, until browned, 8-10 minutes, turning and basting occasionally with the remaining sauce.