Combine the rub ingredients in a small bowl - smoked paprika, garlic powder, onion powder, ground mustard powder, brown sugar, salt, chili powder and black pepper. Mix well until evenly blended.
Rub the seasoning generously over your boneless pork ribs, ensuring each piece is coated well.
Spray the slow cooker with non-stick cooking spray. Pour ½ of BBQ sauce in the bottom of the cooking vessel. Place the seasoned ribs in the slow cooker and top with ½ cup of barbecue sauce. Cook on low for 6–8 hours or high for 3–4 hours until tender.
Remove from the crockpot. Slather the ribs with additional barbecue sauce and cover with foil. Allow to rest for 15 minutes.
Optional step - place the saucy ribs on a broiler pan and place under the broiler for 2 minutes until the edges caramalize and get crispy for that just off the bbq flavor! (Although I call this optional, don't skip this step!)