Almost every tenor uke that is made in Hawaii and is sent to the mainland goes in a cardboard box in an aeroplane, most custom ukes are sent all over the planet in cardboard boxes, often they are in transit for two or more weeks, going through Customs Stores, post offices, shipping depots etc. A few don't make it and get sent back for repairs, but most arrive safely. They don't get carried on board and put in an overhead locker, they just go in the hold with the rest of the mail. Probably every tenor that is sold some distance from where it was made has been sent on an aeroplane in a cardboard box. Sometimes I think a cardboard box is better than a hard case because there is no illusion of strength in the cardboard and most people will take more care with a cardboard box than a seemingly bullet proof hard case.