Not familiar with the Mastercraft seats (whatza matta, you no lika our stuff?). But most seats don't come with belts, and you're expected to use stock. That's for a variety of reasons, liabilities, and what not. That's not always true of racing seats, but even there you're expected to bolt your own in. Can't imagine there's such a thing as a rear racing seat. I'm guessing Mastercraft expects you to reuse the stock.