Are you covering the plants? If the area is getting damp alot, i would try to find something to keep the plants out of that element. Especially when flowering. Also, I believe if they are being overwatered or sitting in still water that can cause powdered mold also.

I was some growing some querkly indoor and the water wasn't draining properly....by sitting in the still water, my plants starting getting powdered mold all over. I wasn't even sure what it was at first. Had to completely toss one plant and it pretty much ruined 2 others (barely pulled a 1/2 oz off of 2 plants)