That's awesome! I wonder if a centrifugal fan would be better than the axial fans though. Centrifugal fans, IIRC, can handle resistance better than axial fans. They're better for forcing air through a filter. They're probably louder though, so it's a tradeoff. If I was building something like this and I owned a house, I might build a centrifugal fan, like a Fantech FR100 or something, into the attic suspended by elastic like I did for my old grow room. You could get great airflow with relatively little noise.