Correct me if I'm wrong, but a given product will have multiple instances. Let's assume a can of oil. We can define all the properties about that can of oil, but, we don't have one can that we put into a shipping box. We have lots of cans that go into lots of shipping boxes. Based on that, you probably need some sort of Inventory table (or maybe just a counter on the Product table, disagreement can be had here) that defines what you're shipping. Then, the second design, multiple products to multiple shipping boxes, makes more sense.