High relative humidity is what mold needs to grow. Get a good % relative humidity meter and monitor the crawlspace. Plus 60%RH grows mold. The %RH goes up when it is wet and warm outside, because moisture enters from outside. When the %RH goes to +70% RH, close the vents and the %RH will decline. If the %RH is still above 60%RH, get a dehumidifier. 50% RH is perfect for storage and no mold. This requires closed vents and 50 pints of dehumidification per 1,000 FT^2 of space.