Silica supplements like Silica Blast help protect against the damage of mildew, among other things.

But treat the CAUSE, which is usually a large swing between night/day temps resulting in dewfall. If you are indoors, add a space heater for night.

SMC is safe to use during flower.

Serenade or another source of B. subtilis is also safe in flower.

Your drying room should not be humid enough to allow pm to keep forming. I'd hang in a room that has a/c and also some type of air purifier that is meant to reduce spores and allergens.