I coated the concrete blocks of my foundation with Drylok Masonry Waterproofer. The latex version goes on just like paint and is easy to clean up. 4 gallons was more than enough to cover my small foundation.
Drylok is supposed to prevent water from penetrating, so it might help keep the crawlspace concrete blocks dry. I like the bright white color and Marshall thinks it will last a long time, so maintenance won't be a problem.