Here is how I ship shrimp.
Place one or two crayfish in a Kordon breath bag, with a small wad of boiled yarn. Make sure that the bags have as little air as possible. The yarn is important, it gives the crayfish something to hold onto, and not die from the stress of constant swimming. Take 1" foam insulation and create a box that fits tightly inside the box you will ship the crayfish in. Next use foam core poster board, or cardboard to make dividers, similar to a jewelry box. Make each compartment the same size as a filled bag. Next take crumpled newspaper and lightly spray it with water. Fill any space left in the inner foam box, so the breath bags do not move.
If you're going to be shipping someplace cold, you may need to include heat packs. If you use a heat pack, make a cutout in the outer part of the foam box. Next make slits so the cutout is connected to the inner compartment of the foam box. Immediately prior to shipping, activate the heat pack, tape it in the cutout, then tape a folded sheet of aluminum foil over the cutout (help reflects the heat back. Tape the outer cardboard box shut and hand it to the FedEx/UPS/USPS deliveryman.
It's best to ship on Mondays. You can ship anywhere in the US using USPS Priority boxes, and if you ship Monday, your shipment will not sit in a post office over a weekend.
Good luck
