It’s not the house my friend. I really do mean this in the best possible way but I can’t help but think you’re perhaps looking at it the wrong way. The spores are everywhere, in every state, in every house, humid south to the Arizona desert. You gonna microban your plants every day? It’s the conditions of the grow. If conditions are favorable, it will come back, no matter what you do, no matter how diligent you are.
I’d hate to see someone give up growing entirely over a little easily-preventable and more easily-treated mildew.
Think of it like algae. If you have a constantly nutrient rich wet spot under lights, you will get algae no matter how clean your house is, or where you live. Unless you have actual biohazard air systems, it will get in, matter of time.