To make this gluten free, I make my own breadcrumbs with gluten-free bread (such as Udi's(R)).
You can also cook this on the stovetop instead of in a slow cooker, if preferred. Cook sauce for 1 hour in a large saucepan over low heat, stirring often to avoid catching on the bottom. Then add meatballs and cook for until cooked thoroughly, about 1 more hour.
Use the meatballs for meatball subs. Or, omit the sauce, and pan-fry the meatballs and serve them with risotto, fresh tomatoes, and Parmesan.