here is my experience with storing/using ply in a damp climate: (can't get
much damper than here in the US Pac. NW)

If is store any ply in outside storage (sheltered from rain) the moisture
content raised to the point that polyester resins don't penetrate/bond
properly. However, if I bring the ply pieces into the heated shop for a
couple days, the surface plys seem to return to a exceptable moisture
content..

I use a moisture meter to verify this and note that in the outside storage,
during cold weather, the moisture content of the surface ply will go as
high as 18 to 20%, while ply that remains in heated storage stays at about
12 to 15%.

If I purchase new sheets of ply, from a stack of sheets, any sheet other
than the top sheet will also be at 12 to 15%.

Bottom line, if your going to have your partially finished boat in an
unheated barn and your humidity is anything like I have here, you will have
to wait until warm weather before doing any taping of seams.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions