I think clamping the pneumatic hinges is a good idea.  A hard crease
is a good thing in the hinge because it allows the pneumatic to open
and close more easily.  I use binder clips because they apply an ideal
amount of spring tension and not too much.  Binder clips are also
inexpensive.  I place strips of Mylar in the hinge area while gluing
so the two pneumatic boards don't get glued together.  I hold the
pneumatics closed with rubber bands to better recover the backs of the
pneumatics.

To recover the backs of the pneumatics the open end has to be closed
or the pneumatic will be less flexible.  The ideal sized rubber bands
will not cause a hard crease in the open end of the pneumatic, which
could shorten its life.  I carefully apply the glue to the back of the
pneumatic so it does not wind up in the hinge creating less
flexibility.

Bill Maguire