I have never heard of using comic book backing boards with fabric - take a peek at the picture below. You can buy these at your local comic book store or on Amazon or eBay. They are acid free and economical.
A pack of 100 run around $10.00
http://www.amazon.com/Ultrapro-Silve...1851687&sr=8-2
The fabric starts folded selvage to selvage then fold it in half to the selvage again. fold over the board and use straight pins to secure
thought I would share
