Make the box triangular (end profile). It is way stronger than a square or retangular box and they cant stack a bunch of heavy stuff on it during shipping.
Ben ... I just refunded your PayPal payment. I tried to fabricate a box today and it did not turn out well so I am giving up. If you still want the part you can have it for $40 + actual packing and shipping charges at the UPS store. I am guessing it is going to be more than $15 for packing and shipping but they will do it right. Sorry ..... Dan