You could try adapting comic book preservation 
methods to dougas, but it'll be easier with 
dougas since you only have to worry about one 
piece of paper.

After reading through several sites, it seems 
like you would need a few things for douga.

1) acid-free backing board (make sure the entire 
board is acid-free, not just the face)

2) pH neutral paper to absorb any acid, or better 
yet, pH basic buffered paper.  Backing boards 
with activated charcoal can also absorb acid.

3) archival mylar envelope

That's if you're totally gung ho about storing 
paper.  Right now, I just keep my cels and douga 
in polypro. or mylar bags in a cel book (with 
cels never touching the douga).