Melisse, the question is where is the moisture coming from. If it is from the tub due to poorly applied or deteriorated caulk, then killing the mold, drying out the area, and recaulking (use a caulk with a mildewcide) should work. If, on the other hand, the moisture is comming from the crawlspace, you will have to solve that problem. Techniques for this are similar maintaining a dry basement (check out article in last issue of Fine Homebuilding (Aug?)) except that the additional mesaure of sealing the crawl- space ground with poly (Tu-Tuf is best) may be undertaken. When the moisture is gone so will the mold and mildew, not before. Good luck.