I would use the 8x8x7 box. Place the tortoise in a cloth bag that is tied shut. Pack him in with paper towel or cloth to keep him from sliding around. I would recommend you dropping the boss off at the nearest fedex center that accepts live animals. This is normally a shipping center, the local stores that accept fedex packages cannot accept live animals. On @TechnoCheese s end, ship as a "hold for pickup at facility". And go pick it up so it does not have to ride in a truck and wait for the driver to make it to your location. On the website when you book the shipment, there is a tool to find the nearest facility you can pick up a live animal.There are 5 different shipping kits, but the suggested sizes are for lizards, snakes, and geckos. What size would be best to ship Piglet (the Russian tortoise) in? His shell measures 5" from head to tail.