So here is the fan I picked up.

We have a re-sell shop that have all sorts of items from home re-models. It was a $1.25

Here the area for the booth. The concrete shelf it sits on is actually what they call a "cap" around here. It was poured to reinforce this old foundation back in the early 90's when the entire house was rebuilt. Now you know why the oval track is so high :)
Behind it was a window. A very poor window as it let cold air in so I sealed it with OSB when I first started to get the mancave ready for racing.

Which is sealed on the outside as well. The vent will be here.
Now onto the box construction.