To brine ribs, dissolve salt and brown sugar in 4 quarts cold water in a stockpot or large container; add ribs to brine. Marinate in the refrigerator for one hour.
Remove ribs from brine; pat dry with paper towels.
Combine spice rub ingredients in a small bowl (or use your own spice rub).
Cover ribs liberally with spice rub.
Cover; refrigerate ribs at least 2 hours or overnight. *
Remove ribs from refrigerator; bring to room temperature for at least 30 minutes up to an hour.
Line baking sheet with heavy-duty foil, if desired.**
Place 1/2 cup water in baking sheet; place cooking rack inside the pan.
Spray cooking rack liberally with cooking spray.
Place ribs directly on cooking rack; cover entire baking sheet with heavy-duty foil, folding edges underneath pan to seal.
Bake ribs for 8 hours without opening door.
Remove ribs from oven; let stand, covered, for at least 30 minutes to allow juices to settle.
Remove foil; brush ribs with commercial BBQ sauce.
Return ribs to oven and broil on top rack of oven for 5 minutes or until glazed.
Cut ribs into individual servings.
Serve with additional barbecue sauce if desired.
*If you want a sauce (fond) of drippings to form, leave the aluminum foil off the bottom of the sheet. If you want to discard the drippings, use the foil. **If freezing the ribs to cook later, freeze them after brining and applying dry rub.