Re pouch discs and Hydrophane, I would strongly doubt that an adhesive
which sticks to leather which has been treated with Hydrophane is
practical -- if indeed it's available.

Hydrophane seems to leave a very slight but very effective waxy residue
which does what the manufacturers claim it does for leather.  However,
because it is absorbed well (the leather acts like blotting paper),
and pouch discs should only be attached by a small point of glue in
the centre, inflating the pouch by suitable means whilst applying with
a small brush should do the trick.

Regards,
Paul Morris - recent Hydrophane convert