A moisture scrubber is a box you install in a crawlspace vent. The
vent fans on the other side of the crawl space pull air through the
scrubber. The scrubber has coils in it over which air passes, and this
is supposed to condense water out of the air. The water is then
supposed to drain back out of the crawlspace. I can't say for sure
whether they works very well yet, as I had them installed at the end of
last summer, so they haven't gone through the hot part of the summer
yet. But my crawlspace has certainly been far more dry since they were
installed. They were installed by a local company here in Knoxville,
TN, but here is the url for the company that makes them:
http://www.ventthecrawl.com