So I read your post, and came across this video on Youtube:

https://www.youtube.com/watch?v=59I1KvEpMco.  

He concentrates on a 3-season approach, however  I'm envisioning a modified box that still vents out the top, but vents to a 3" PVC pipe, inlined coupled to a 4" fan.  This way I could run the box inside the house.  I have a pipe available to me in my utility room that is vented to the outside. A fan can be put inline.   How many CFMs does one need for a 6-card rig of 1080Tis or for multiple rigs of Tis?