TJ,
Carol had the system down pat she may be able to tell you. She used standard USPS 2 day shipping in a medium (maybe large?) flat rate box. she had green foam board I'd guess 3/8" thickness cut to line the bottom and inside 4 sides of the box. Then a bag with maybe only 4" of water in the bottom with my PK shrimp, nothing but the native water they were in that looked a bit greenish, but no plants, leaves etc. Not sure if they needed oxygen, perhaps she put some in she would know. The bag was not under any pressure like my other shipped items come when there is oxygen in the bags. Then a green styrofoam lid and taped the top. It helped that she shipped when the ambient temp was cooler (spring or fall best).

She said flat rate using priority mail was 2 day delivery from her zip to mine in Michigan. Weather was cool, came on time, no losses. USPS flat rate boxes might be the ticket for at least some customers. I think my shipping was $40-45 if I recall.

I'd love to place another order.

Bill D your instructions are good, they apply to scuds (Gammarus sp)

I am told by sellers that ghost shrimp or PK shrimp are larger and more tolerant of lower oxygen conditions that may occur during shipping.

Scuds are smaller and more dependent on water and oxygen conditions to be right for survival.

The quote below is from an email I had from a seller of scuds:

PK Shrimp also require less oxygen than adult freshwater scuds (Gammarus sp). I would not ship a gallon of Gammarus in a flat rate box nor a gallon that would take two days to arrive...you would have dead shrimp. We ship a gallon of Gammarus in a 5 gallon styro pail which is 1 gallon of shrimp and 4 gallons of water...if this package arrives in two days due to UPS messing up the order, then the shrimp are dead.