MLD wrote:

The way that we used to get moisture out of small inaccessible areas (like
a bellows) was to pull a vacuum (which would evaporate the moisture) and
basically suck it out. Not a practical solution for this problem...

How about a repetitive partial vacuum and a source of dry air, eg a box full
of desiccant bags? How many times do we have to squeeze a bellows to remove
5% of the air from a window cavity, with a check valve and a vacuum breaker
that allow dry air to replace expelled air when the bellows is released, if
we want to lower the cavity dew point from 50 to 10 F?

Nick