If you live in the SE USA, you should cover the earth in your crawlspace. When the outside dewpoints are high close your vents for sure to avoid all the outdoor humidity from entering and condensing on the bottom of the floor and on the plastic. I suggest covering the earth in crawlspace anyplace that grass grows. Monitor the relative humidity in your crawlspace. When +70% RH, you are on edge of growing mold. Should be avoided.