areyou intending to put more than 1 in a box?
When I ship pcb's (1 at a time), I put it in an antistatic bag. Then I wrap it very well with bubble wrap. Then I find a box big enough that I can put foam cushion around the 4 corners of hte pcb. Then I put additional firm cardboard inside the box to help protect it.
I put additional heavy duty padding between the front and back of the board and the box.
When I am done, you can throw my box against the wall and hit it with a baseball bat, and not hurt the pcb.
Takes a little more time, costs a few more bucks, but I can imagine the hassle of dealing with a pissed of receiver and the shipper for insurance is a way bigger pain in the ass.
When I have shipped 10 boards in 1 box. I wrapped each one in an antistatic bag, wrapped each one in bubble wrap, then I put a ton of padding around the inside of the box and between each board. Same thing, kick the box, throw it off the top of a house, not going to hurt it.
This should be your foundation for shipping boards. Make it impossible to damage them. when you shake the box, nothing should be moving inside after a good pack job.