Hi Danger
I used the 2 speed version of this motor when I made my downdraft booth a year or so ago.
I ended up making a ring out of MDF (thickness can vary) and mounted the motor on the underside (outside) of the box. Only the blower cage is exposed to the fumes the actual motor is well outside where the air can cool the motor. They get very warm if left on for any length of time.
Your booth will be a backdraft, but I would think mounting the motor would be similar only on the back.
I use two filters the first (stage) uses a plastic mesh universal filter available at Lowe's(cut to size) then directly underneath that filter say about 2" underneath I use a 16x 25 pleated furnace filter. Then another couple of inches below that there is a 6" diameter hole thru the bottom of the box and you can see the blower wheel/cage.
I also use a 6" exhaust out to a crank out window. The end of the exhaust is pushed thru 2" of blue board and sealed wit caulking. The blue board is in place of the window screen and can be easily removed with no damaged to the window.
I only mention the exhaust because it is a critical part of the booth. I'm sure yours will differ but give it careful consideration. Diameter and length of run as well as bends have a noticeable effect on efficiency.
Mine has worked just great. I spray allot of lacquer and never ever smell it when not wearing a respirator. I do recommend a respirator at all times. Its just that sometimes I'm lazy just want to paint something quick
If you think pictures would be helpful even though mine is a downdraft and your making a backdraft.. let me know
Good luck