In addition to the UV glass, make sure all the 
other materials you use are acid-free and/or
archival quality.  My only issue with the laser
copy background would be the paper it would be
printed on and the inks used.  Optimally, both
should be acid-free if you are going to be placing
your cel directly on it.  If not, I would suggest
a clear sheet of acetate or acid free mylar placed
between the cel and the laser copy background as
a buffer and it should be replaced every few 
years.

Jen