Oh, crap.  Manilla envelope... PM mailer...

*thinks back to how she used to pack cels, before 
she knew WAY better*

Was that me, Misha?  If so, I owe you an apology, 
a couple boxes of Pocky, and an opportunity to 
beat me senseless.  :(

These days, I pack inside a sealed cel bag, which 
goes into a flat 1097 Priority Mail box, which is 
taped shut and IN TURN goes into a larger 1095 
Priority Mail box, which is glued AND taped shut.  
One thing's for damn sure, though... I make sure 
not to put tape anywhere near the pull strips.  
They're the best way to get something out of one 
of those boxes intact.