^Keep the fans running at night, too. I've seen many set on the same timer as their lights, turing off when they do, which can cause problems.
I like to keep my humidity around 35-45%,(usually on the lower end) during flowering, and haven't had any mold/rot issues, yet... *knocks on wood*
Also,...it helps if you back off on the watering, a little, compared to vegging. This is dependant on your medium, and it's drainage qualities, of course....