[skyking]

Originally Posted by freebeard

In my case there are three 14" square roof vents, with a whole house fan on the center one. So it can suck up on the center one and blow down on the two ends. It may not be as efficient but it works with what's there.

I think that's a brilliant idea for a grounded TT with holes in the roof already. Maybe a black painted box with recycled sliding glass door cartridges arranged as a pitched roof, with 6" metal ducting going lengthways to a plenum on each end and the middle. Insulate the box with 2" foam, paint the tubes and background black.
I think it would cook you quite nicely on the shoulder seasons in the PNW, and act as a bit of insulation in the dark of night when you close it all off.