In that case it does make sense, and if it works for you to keep the optimal conditions then i'd say you did a good job. I apologize for trying to teach you something you already knew, i thought maybe you mixed up the ventilation system, i've seen people mix it up before so it's not uncommon
I was going to suggest you to use reptile heaters or portable AC unit and utilize the standard way of ventilation, but you say it's 30F during night in April, holy shit.. Then your best bet would be to keep doing what you do and use Neem oil as prevention, or citric acid as others mentioned. Maybe UVB light can help prevent mold, although that's debatable. Good luck, hopefully you sort it out!