The good news is you didn't mention that there was major puddling under the plastic. If this was the case, I'd approach your question a bit differently.
Beings you covered the dirt w/plastic, any moisture that rises up out of the ground is going to condense on the underside of the plastic. This is normal. Do what you can to 'secure' the edges and prevent them from curling up. I wouldn't lay anything like carpet or wood on the 'center' areas of the plastic because they ABSORBE water/moisture. This could be the source of your 'smell'. If anything, use 3/4" gravel around the edges and center (if you want.) If you're going to use wood, use Pressure Treated wood. I wouldn't suggest using fans or anything to dry out the moisture. If you can understand the physics of the situation, any air being drawn by the fan that's WARMER (and it need only be RELATIVELY warmer) than the air in the crawl will have its moisture CONDENSE OUT on any surface that's COOLER. So, if you're drawing air that's 40 degrees into a crawl that's 38 degrees, the moisture in the 40 degree air will condense out on surfaces that are cooler than it (which would be 'things' in the crawl that are at 38 degress.) See what I mean? And by using a fan, you dramatically speed up that occurrance.
Again, toss anything that's absorbing moisture and stop the fan and get some 'stuff' to keep the plastic down. My best to ya and hope this helps.