Sketches and douga aren't like cels... they 
don't stick together, you can easily store them 
in a stack, and the preservation methods of 
paper are pretty much known and agreed upon.  
Our cels may all fade away, but there's no 
reason why the sketches shouldn't last for 
generations.

I've opted for archival safe boxes with buffered 
liners to store my sketches in.  I bag up the 
sketches in cel bags with the flaps cut off.  
There's no need to seal up paper when it's 
stored in the buffer box. Multilayer sketches 
and entire cut scenes can all go in the same 
bag... no need to go bag crazy.  Anything on 
colored paper gets stored in a seperate bag, as 
I am always worried that these may be more 
acidic and the colors might leech out over 
time.  And then I just stack the sketches in the 
box.  Easy peasy. As long as you stack similarly 
sized things together, it shouldn't be a 
problem.  Label the side of the box, and you're 
good to go.

I suppose that's not as convienent to flip 
though as a portfolio album might be, but there 
are trade-offs in everything.  Frankly, I think 
Itoyas (and albums in general) are a lousy way 
to store anything, cels included, and are really 
only good for carrying stuff to show off at a 
con.