well, i dont think baking soda would help. i thought ppl use baking soda to absorb odors (not moisture).. the mold will need to be removed by you--how close are the cabinets to the tank and/or sump? im assuming you mean the cabinet doors of your tank stand?
if i were you, id go to lowes or home depot, get some damp-rid and place an open container of that in there to absorb any moisture that is in the air--it will cut down on the moisture, and i would carefully spray some tilex mold and mildew removal on a rag (away from the tank--preferably in another room lol) and use that damp rag to rub the mildew/mold to kill it... i wouldnt know what else to do that might work.
someone may give you better advice, but thats just what id do..