Bob,
Depending on where you are, an exhaust fan wired to a dehumidistat can
be a very ad idea. In this area, the bug companies love to do it.
Then the floor joists start to rot and the finger pointing begins.

In most areas it will help in the winter if it does not frreze the
pipes. In humid climates, it is about the worst thing you can do.

The OP has the right idea.

The Radio Shack units are reasonably accurate, at least the ones I have
checked. They have up to 3 remote sensors. I norm,ally use Hobo Data
Loggers from Onset Computer Corp. Then I can leave them in the
crawlspace for a couple weeks and download a graph to my computer for a
permanent record.

For more information see this link on Crawlspace problems:

http://www.contractingbusiness.com/C...S=&NI L=false

Stretch