Preheat a 4-quart slow cooker on high for 10 minutes and heat the marinara and broth until steaming.
Pour the hot sauce mixture into the cooker, stir in the Italian seasoning and add the thawed fully cooked meatballs.
Cover and cook on high for 20 to 23 minutes, stirring once, until the meatball centers reach 165°F.
Divide the meatballs and thick marinara among the split rolls and top each with 2 provolone slices.
Broil the open subs for 1 to 2 minutes, until the provolone bubbles, then close and serve.
