I used aviation snips to cut along the bottom portion of the ducting. No turning back now! The initial cuts do look kind of rough.
Heres how it looks with the middle cut out. The sheet metal is *extremely* sharp. I used and angle grinder to smooth the edges.
I then cut 45 degree angles in the corners, and using a 1x4" as a guide and a rubber mallet, hammered out a lip on the inside which should help in condensation. It also cleans up the look quite a bit.
Here's the finished look of the lip... I was pleased with how it turned out.
The whole thing is actually much more rigid then I had originally thoguht; I probably didn't need the 2x4 framing, although it will probably make mounting the whole hood easier.
Right now I'm a little stuck, I have a 6" blower fan and a non-circular 3.5-4" hole in the cold room that I plan on venting out through. I'll need to somehow reduce from 6" to 3" for running a length of pipe oudoors... If anyone has any ideas for this I'm all ears!
I was actually considering buying a different model 4" fan and using a 4" to 3" reducer as a backup plan.
Aviation Snips: $18.99