Dan, a couple of tips learned the hard way...

1) Be sure to immobilize the chip by taping down the flip inside the padded envelope.

2) Use an extra layer of something (cardboard, paper, whatever) to protect the chip inside the padded envelope.

3) Make sure you tape down the fold-over flap on the outside of the padded envelope.

4) I would have the package metered at your local post office - and ask them to hand cancel it - this will keep the padded envelope from going through a machine and possibly damaging the chip within.

Just a couple suggestions.