I'm getting a lot of condensate on my HVAC ducts that run though my first floor (and HVAC blower) especially in July / August when humidity levels are outrageous (in NJ). The 1st floor space space is rather frigid as one face of it is below grade so it's hard to convince the occupants to open the registers to dry it out (at least not without opening the windows and letting the humid air back in). However even on days when humidity is lower, I can occasionally notice a small amount of condensate build up which has clearly led to mold growth under the previous owners care. Further compounding things is the natural tendency for the cold air to make its way back down to the ground floor via the small gaps near return / air filter area and in the registers themselves.
I know most people say to just insulate it, but the previous owner did this in a few places (with neoprene peel-n-stick in some places, and standard batt in others) and it looks terrible, and it appears with standard batt insulation just provides another surface for mold to grow on.
Is there any sort of water repelling coating that that I could use to prevent the condensate from building up in the first place the way RainX works on car windows?
Is there some other trick I should be using to reduce humidity or condensate build up on the duct work?