With the fan directly below the charcoal, doesn't it blow ash everywhere?
I can chime in here. I use my HM v4 with my 22" kettle / smokenator combo frequently. I drilled a 3/4" hole directly under the coal chamber of the smokenator and plugged in the fan with a copper tube. PID settings fiddling and max blower output at around 15% and it works like a charm. I've kind of wanted to do a little more interesting stuff like pump the fan into something like this:
http://www.homedepot.com/p/SharkBite-3-4-in-Barb-x-3-4-in-Barb-Copper-Manifold-with-3-1-2-in-Barbs-22784/202721983
I haven't had time for that because the WSM has been getting most of the winter action.
However, you should also look at the "air burners" that folks have come up with. You pretty much have to drill a hole in the kettles no matter what because the ash-catcher mechanism prevents a lot of the dog bowl solutions from working.