Pete's reference is for transfer of ownership which doesn't apply to sending your own firearm to the mfr for repair, and the return shipping label sent by H&R is a UPS label, not USPS. Best advice is break it down and ship it in a shorter box within another box, use lots of packing so the parts can't touch each other or possibly move, the only markings on the outside should be the shipping label and box certification that most boxes have on the bottom, a black marker or duct tape work well to cover unnecessary markings. Wrapping with paper isn't a good idea unless well sealed, if it's gets removed in handling, the shipping label is gone with it and the package becomes undeliverable and lost.
Tim