OK. Don't worry about it. The screened vent everyone tells you to have for your dubia bin is primarily for letting moisture escape. Dubia will create quite a bit of humidity on their own. (All that dried poop was once moist.) Cover up about 90-95% of your vent. It will help keep a little heat in, too.
When I first started a colony, I kept hearing warnings to get the fruit out before mold would grow on it. Well, my fruit dried out well before there was any chance for mold to grow. The low humidity was never a problem with the colony.