Well, here goes.  At the risk of suffering the wrath of you restoration
purists out there, I think I have discovered an inexpensive gasket
material for use on wind chests and other pneumatic "boxes" and would
like to share with those that may find it useful.

It's available at Kragen Auto Supply stores and is called a "Drying
Cloth" (Artificial Chamois), made by Viking Car Care.  Comes in 18 X 20
inch sheets for $4.95 each.  The stuff seems to compress nicely to
conform to minor surface irregularities.  I expect some very minor
seepage, but not enough to do harm in this application.

I am not using it on a restoration project, just on new construction
for several organ pipe wind chests and reservoirs, so anything goes,
right ?

Also, have found that Fusible Fleece (Polyester), purchased at the
local yardage store, works fine for mechanical damping of pneumatics
(silencing cushions) and for lining the holes in the top support plate
(I forget its formal name) for tapered base metal organ pipes.  This
stuff is about 3/16 inch thick uncompressed and is quite soft.  Paid
$3.49 for a big 23 X 34 inch sheet.

One final blow to the purists: I am not sticking these materials on
with hot glue !  Sorry about that...

Regards

Lee Roan