What to use for backing?

[sqphoto]

I'm working on putting together an 11x14 portfolio in a clam shell box that is 2 inches deep. I print on Ilford fiber paper and I make square format images that are 9 and 1/2 inches.
Obviously, I'm trying to NOT have the box full of mat board. I'd like to have as many prints as possible - but I'd like for them to be as flat as possible.
I have heard that some photographers have dry mounted on 2 ply board and they are flat.
I have also heard that some photographers use a second piece of fiber paper, run it through fix only, and then dry mount the backs of both pieces of paper together, and they are flat also.
I went through all of the previous discussion on this matter and didn't find an answer. Anybody got a system that they have tried and it works? Then - how did you do it? Thanks. Michael Atherton

 

[Jeremy]

I just completed a 17 print portfolio (with an 18th title page print) that is drymounted to 2ply and overmatted with 4-ply. The images were then placed in clearbags and it all fits into a 2" black, clamshell portfolio.