Line slow cooker with a slow cooker liner (optional) and then spray with non-stick cooking spray.
In a small bowl, mix together mustard, salt, garlic powder, seasoned salt, brown sugar, pepper, and cayenne pepper.
Rub both sides of rack of ribs with seasoning mixture. Cut ribs into 4-6 pieces and place in slow cooker. Pour water in the bottom of the slow cooker.
Cook ribs in crock pot on high 4-6 hours. Add BBQ sauce and then cook for an additional 1-2 hours.
Remove ribs from crock pot and serve.
Notes
If you want to caramelize your BBQ sauce on the ribs, line a cookie sheet with aluminum foil, place ribs on top, and brush with more BBQ sauce. Place pan in oven preheated to 400 degrees and cook for 8-10 minutes.