Gene,  Fear not, piano rolls _are_ media mail.  If the clerk will
only check, they are listed in the regulations as "Musical Recordings."

I have shipped and received many rolls as "Media Mail" and have only
had one bad experience, when the box disappeared in the Richmond,
California, distribution center.  (Sad to say, it has a reputation
for this).  I did get about half the rolls back five months later with
a note from the USPS that the box was "not deliverable as addressed."

Hmmm -- it was sent with a USPS generated label, so who knows?!  And,
yes, it had tracking!  (Media mail can be sent with tracking.)

Good luck!
David Dewey