All the earth should be covered by air tight plastic. Get it to lay tight to the earth with a little gravel. Use twice the recommended dehumidification to assure 50%RH. Get a minimum 50 pint unit. Check EPA web site for high efficiency dehumidifiers, http://www.energystar.gov/ia/products/prod_lists/dehumid_prod_list.xls Many people suggest no insulation between the home and crawlspace. May be vaccum the mold off with exhaust to outside?