Can I decorate a USPS flat rate box?

My husband is in Kuwait and when he is away my children and I decorate the outsides of the packages that we send him. We usually send via DHL & USPS regular mail when he's away from home, but still in the states. USPS now has APO/FPO specially priced flat rate boxes for overseas. I can' find anything on the USPS website. Does anyone know if I can decorate the outside of these boxes?