That's what I was thinking.
Should you use an explosion proof motor?
if the motor is in the exhaust stream, it should be. if you have a fan in the exhaust stream (belt driven), it should be spark resistant. You should look for 100+ ft per minute at the filter bank. Furnace filters work well. I use 16x25.
My "booth" is a little larger, but I can spray larger things (not a car, but larger things).
The plenum is nothing more than an air tight box. I use an explosion proof shuttered exhaust fan. I don't spray every day, but the bench booth I created keeps the rest of the shop clean.
Mine is in my parts washer / blast cabinet / paint closet. It seconds for a fume exhaust when using the parts washer or blast cabinet.