Ok so I'm having all my reptiles shipped out to join me here in Georgia all the way from Colorado. This is my very first time shipping anything, and I have some questions about the packaging itself, especially about what kinds of heat packs I should use.

I would buy some 40 hour ones, but I'm concerned that while they'll be helpful for the first leg of the journey in so-cold-Colorado, it could make things too hot later on once they get to the second half of their journey in a-lot-warmer-Georgia. The only shorter length heat packs I could find were the 8 and 16 hours ones which are specifically hand warmers. Would those work perchance?
Or a better question, do I even need heat packs at all if the final destination is warm enough?