What are the best ways to ship oversized cels?  
With the normal ones, I usually just put them in 
hard photo mailers (so far none have gotten 
damaged...) but with some imminent 18x24"  cels 
coming along, what should I do?  

The only thing I can think of is to have them 
framed and then send them in a box, but that 
can't be the only way -_-

Thanks!