For the rib rub: Combine the salt, sugar, garlic powder, cumin, paprika, black pepper, cayenne and chile powder in a medium bowl and mix well.
For the barbecue ribs: Heat a charcoal or gas grill.
Rinse the ribs and dry them well with paper towels. Coat the ribs with the rib rub to form a paste and wrap them in plastic wrap. Punch about 20 holes in the plastic on both sides of the ribs.
Warm the mesquite chips and cherry wood chips in a pot until smoking.
Transfer the smoking chips to one of the roasting pans. Punch about 10 to 15 holes in a second roasting pan and set on top of the pan with the chips. Place the plastic-wrapped ribs into the pan. Cover with the third roasting pan.
Place onto low heat and smoke until tender, keeping the smoking temperature around 175 degrees F, for 4 to 6 hours.
Serve with your favorite barbecue sauce or enjoy the ribs on their own!