I use 6x6x6 boxes and then cut 3/4 styro to line the bottom sides and top
I use 2 mil bags. Just enough water to cover the frag and then tie off the bag. No air required in the bag when shipping corals
I then take 4-5 frags and put them in a larger bag and then into one more bag so there is 3 layers of protection.
Use 40 hr heat packs from here when necessary.
http://lllreptile.com/store/catalog...king-material/-/disposable-40-hour-heat-pack/
I also fill any void areas in the box with small pieces of styro
I use FedEx standard overnight
I don't feel that the extra money for the priority overnight is necessary
One of the biggest tips for shipping coral is only ship quality well healed frags. Look at the frags you are shipping and look at them as if you were the one receiving them. Don't ship unhealthy fresh cuts and you will have great success
It is better to do it right the first time then having to reship
And another thing. Be prepared for losses. Sometimes no matter how well you pack and how quality your coral is. You will have doas from time to time. And communication with the person recieving the corals will
Solve a lot of headaches
Good luck!!
Bob