Code, you'll need a box that will allow space for the cushiploning of the plant.
Prior to shipping, you'll want to depot, clean and dry.
You'll want plenty of newspaper, packing paper, and possibly, styrofoam.
You'll want that plant to ship dry or spores and rot can be invited.
I would give any Ping that I shipped plenty of extra room for cushion and I would do a box within a box of styro.Id hate to break any spines. For me, I don't think Id settle for anything less than 2 inches of foam/paper packing.
Are you shopping the group together? Will you be saving some for yourself?