I'm not sure about other methods. I only have one 
cel book and it's an Itoya Easel book. I'm very 
happy with it and I think it looks the nicest for 
presentation. 

I'd be curious to see any research that compares 
storage books to storage boxes in terms of 
preservation. I know that some people have used 
an ordinary shoebox and gotten great results. 

My only concern would be that the cels would lie 
flat against each other. According to the 
guidelines at Nichibei, cels should be stored 
vertically so that they are flat and not exerting 
pressure on each other. To avoid this, I always 
keep my cel book upright when storing it. This 
would also probably lessen the problem you have 
with your cel book bulging.

Hope this helps!

Fever