I would definitely have the snakes held at the FedEx ship center. They are usually brought in the office as soon as they arrive at the hub and don't sit in the wharehouse waiting to be loaded on a truck. Also this reduces risk of driver delays.
Picking the perfect box size is important. Don't go too small and the snakes won't have to be super close to the heat pack. I would also suggest using Polyfill for packing material.
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