Wrapping the wood itself: If available, first wrap the wooden stock in an old towel or some other really soft fabric. I’ll wrap the finished stock in it when returning to you. Reason: When I ship back to you, I like to wrap the refinished wood in soft fabric as opposed to plastic or hard paper wrapping. Although the finish is plenty cured at that point for handling, it continues to cure (harden) for some time thereafter, up to 2-3 months for total cure. Maximizing care during shipping, therefore, is added insurance no abrading can occur.
Second, wrap the toweled-up stock preferably in bubble wrap– the more the better.
Outer shipping carton: Please use a strong outer carton big enough to allow for ample bubble wrap or other padding material around the wrapped stock. Bubble wrap seems to offer the best protection. A small roll can be gotten cheaply at WalMart’s office supply section, or at Staples, Office Max. Seal carton with strong shipping tape.
For long gunstocks (rifles), as opposed to 2- piece shotgun stocks, if you don’t have a suitable long shipper, the UPS Store sells a 6″ x 6″ x maybe 36″ sturdy shipper that’s well sized for just this purpose.