I have been looking at the Down Draft Hoods. Hurd & Don Godke are the two that come up.
Any comments on either out there? I see the Don Godke one has a adjustable opening at
the top. Ant thoughts on why, when the purpose is to keep heat stable and more smoke in
the chamber?
I have the Traeger 075.
Thanks in advance.. 

I think it works fine at smoking temperatures with that vent closed but needs to be open to reach higher temperatures for baking / roasting. Needs might be a strong word but I think it works better with that vent open at baking temperatures.

There has been a lot of chat on these in other smoking pages. Some say they work. Others find no difference in pit performance. All in the eyes of the beholder.

I just ordered a Don Godke down draft for one of my Traegers.  Looking forward to seeing if it makes a difference. 

 You can try a cheep and dirty method; a section of metal dryer pipe stuck into the stack hole extending across the grate towards the opposite side. It isn't a snug fit in the hole so some smoke travels the original route with most of it going into the pipe..It is

easy to install and  remove for hi temp cooks..If memory serves me well it's a 4" dia. and 2 ft. long.