1. Remove the membrane from the back of the ribs.
2. Mix brown sugar, salt, black pepper, garlic powder, and onion powder in a bowl.
3. Rub the spice mixture all over the ribs.
4. Place the ribs in the slow cooker, meat-side up.
5. Pour BBQ sauce over the ribs.
6. Cover and cook on low for 8 hours.
7. Preheat oven to 375°F (190°C).
8. Transfer ribs to a baking sheet lined with aluminum foil.
9. Brush more BBQ sauce on the ribs.
10. Bake in the preheated oven for 15 minutes, or until the sauce is caramelized.