Not sure how far back people review these posts, but in case anyone saw my first post, I've learned a few things since then:
I appreciate the other responses (vent fan would bring in moisture, and close all vents to prevent condensation), but I'm suspecting what we have is a difference in geography and geology. In the piedmont of NC, it appears my situation is somewhat "normal", and as a result there's a company that's manufacturing a system precisely to vent crawl spaces that have too much moisture. I'm not sure what it's like in the north or western U.S., but down here the humidity/moisture under houses is staggeringly higher than outside (and that's plenty humid). The ATMOX.com site has a fan system with, I think, humidostat (?) controls which, if I'm understanding correctly, vent to the outside when the humidity is higher inside than out, thereby helping to evaporate the moisture.
Not sure I need the whole system described at this site, and please don't interpret this as an endorsement, I have no idea if I'll use the product or if it's silly, but just an FYI that it exists and the problem is common in some parts of the U.S....
Thanks for all the responses to my post, they're much appreciated.