Just put down ` Polythene template ..no commercial value`
Also, as you`re sending it to a Post Office box number, you`re better off to just send it normal [non-track] mail because generally, no-one will sign for receipt when an item needs to be popped into a P.O.Box...... I`ve never had an issue with templates going missing ....just pop a note into it asking John to confirm he`s received it ! Good luck.