Mix together kosher salt, celery salt, black pepper and garlic powder. Rub seasoning mixture generously over ribs. Seal ribs in an airtight container and refrigerate a minimum 1-2 hours, or overnight.
Heat gas grill to 400 degrees Fahrenheit and place the ribs on direct heat for 10 minutes, turning once half way through.
Prepare barbecue sauce by adding all ingredients to a saucepan. Bring to a simmer over low heat and simmer for 10 minutes, stirring frequently.
Remove ribs; baste generously with barbecue sauce. Wrap in heavy aluminum foil and seal tightly.
Grill on indirect heat at 350 degrees for 40 minutes; remove from heat and unwrap. Flip the ribs over, baste again with barbecue sauce, and re-seal aluminum foil. Return to grill on indirect heat at 350 degrees for 35 minutes.
Open foil to expose ribs, and continue grilling for 15 more minutes. Check with meat thermometer to ensure temperature is at least 165 degrees. Ribs are ready to serve!