The biggest issue is not that the box could be empty but in the above case it was never delivered. USPS couldn't assume part of your scheme was hoping USPS would lose your overnight shipment. If it the recipient got an empty box or old lime that's one thing but they can't produce the box to argue their point. I would have argued that until I died. Even without a lawyer after your 50th call and email to the postmaster something will give. The squeaky wheel gets the grease in civil service

 

You can double box using any type of shipping box as long as it does not have any hazardous writing on it. This is according to ParcelPro.