I do it in a 20 x 45bu I am in the PNW and it is just not hot here. Most years we have a couple of days in the 90's about four to six in the 80's the rest high 50's to mid 70's. I don't use fans but roll the sides open to keep the heat from building. No mildew no mites, But then maybe they don't live here anyway.
This is the cheap home built yomatoe house . Sorry I dont have a good pic of the bigger one lost my pictures in a crash.
I also grow in a homade pvc pipe framed hoop house 12 x 45 no roll up sides so I leave the ends out when it gets hot. Again no mildew and no mites
