Water filters UVB too."Glass filters out 95% of all UVB rays unless your tank's glass top has been specially produced for high quality light penetration." Does anyone know if your average tank comes with the special glass? [http://www.futurepets.com/trivia/aquariums-lighting.htm]
I live in North GA with a very similar setup to yours. It is interesting to me as I have NEVER seen any mold as you described on my wood canopy. I have an open top and the only air flow I have is from the small fan in my coralife fixture. Sounds like you just have mold issues in NC.I don't currently use glass tops but I do have a wooden canopy over my tank. One problem I have is a mildew/mold substance growing on the inside wood of my canopy. I don't think I'm getting enough ventilation but I believe a glass top would help cut down on the moisture and thus the mold in the canopy.
Let me say this as well though... I have witnessed fluffy mold substances growing on the underside of glass tops as well. Even in a retail location where the front panel was lifted repeatedly every day in order to sell the tanks inhabitants, the mold was still growing. A quick wipe down with some water and detergent fixed the problem but it always came back. Again, I think it's a high moisture + no air flow = mold.