I do not know what kind of box you are planning to use, but 
there are archival boxes available.  I bought mine from Dick 
Blick, and there are some really big Itoya books availabe too. 
(look at the Utrecht site online.)  If you are planning to put them 
in a drawer, line it with acid-free paper. If you put your cels in 
something that seals, it will also hold moisture from the air in it 
which can cause damage to your cels. I have a cel that appears 
to have been mis-stored in the past and has mold on it.