I think if you go w/o a box that it will get broken or bent at least.
Ask the buyer what he prefers, if you ship it in a door box or whatever I would think shipping costs are going to kill you.
You could cut the bimini in the middle, then it could be rewelded or a pipe connector used to reconnect it ? like I said, that would require talking to the buyer to see if he likes that idea.
How far is the distance to be shipped? could you meet half way?