Yes. Water vapor is a gas. It is intimately mixed with the air and goes
wherever the rest of the air goes. Even in a nominally dry basement water
vapor passes through the concrete foundation walls and floor. The relative
humidity in the plastic container will be the same as that of the air in its
surroundings; unless, of course, the container is initially filled with dry
air and hermetically sealed and even that will likely just extend the time
required to reach equilibrium (like the leaking double pane window units in
my 30 year old house to cite an extreme example).

David Merrill

"RonB" wrote in message
newsQVtf.46522$ih5.46229@dukeread11...
snip.

I doubt that sealing them in a plastic container does that much good.
Might even keep moisture in.