I really do not want to get in a debate about sealing pouches.
I have over 40 years of experience with player pianos and I can
positively tell you that every zephyr pouch equipped player piano
that I have seen was failing due to the zephyr skin pouches.

Currently there is a Wurlitzer organ in my shop that was recently
restored with new valves that are very nice but the zephyr skin
pouches are failing.

The leather that is sold for pouches that is reddish in color (like
the old Robert Morton pouch leather) is sealed leather, hence the red
color.  The tan leather sold today has to be sealed as it is not the
same leather as was available 80 to 100 years ago -- it tears easily
and is porous.  Use whatever pleases you to seal it as it has to be
sealed.  Coinola pianos used rubber cloth for pouches.  I guarantee
you that zephyr skin pouches in the [humid] South will fail.

Don Teach - Shreveport Music Co.
Shreveport, Louisiana