I rebuilt a couple bellows for a crown graphic. I tried to use that Porter's dark cloth but had a very difficult time with it. any glue I tried to use didn't stick well. maybe a good rubbing with alcohol will make it stickier but as it comes nothing stuck to it.
The second bellows used cloth from an old changing bag. That worked much better. It's also thinner so is easier to fold.
Also, most designs show individual pieces of cardstock for the supports. I cut the supports in four long pieces with just a narrow strip holding the individual parts together. It still folded properly but was much easier to handle.