I quite agree with Robbie's comment [120810 MMDigest] about
"student piece" vs. "masterpiece" -- the goal should be to learn
the craft.  My student piece (back in the 1980s) was actually two
pianos restored at the same time.  In trying to learn the craft
I used traditional rubber-coated cotton cloth and hot glue on one,
and Polylon (polyurethane-coated Nylon) and PVC-e on the other.

The piano with the traditional material required constant fiddling
due to leaks, many of which were attributable to the cloth breaking
down at the creases.  The piano with Polylon stopped working just
last year -- the air motor is stiff (which was covered with Bilon).
I used traditional materials on the bellows and reservoirs on both
pianos, which held up quite well in both.

I don't know what this will indicate to you as your best option,
and I know there are much more experienced restorers who will give
both similar and different advice.  The best advise I've ever heard
on this topic, though, is to test the materials.  I wish I had that
wisdom way back when.

Brian Shaw