I do a fair amount of outbound and drop ship ocean shipments.

Normally its required to have: 
Bill of lading: with size and gross weight of order including all packaging material.
Commercial invoice: country of origin, harmonized tariff code, terms of sales, currency type,
Packing/Weight List: Number of packages, Description and items in each package, quantity, net weight, gross weight, package size or volume, Total shipment net weight, gross weight, size or volume.

gross weight would need to be calculated at the pack order page. Due to the fact different sized / weight boxes could be used to fit any number of products. Net weight can be calculated from inventory fields, but gross weight would vary shipment to shipment, box to box. depending on how its packaged.