Ohhh oh, confidence. Just when you get a bit too much of that or start to think you got it down, or thinking its easy, something will happen to cut you down to size, and make you think your a rookie holding a spray gun for the first time again.
Try a search for positive pressure booth. Many do use that sort of setup, and suppose to keep dust from blowing out of cracks or poor seals, and your not drawing paint and solvent through a fan motor. Lots of booth setup information to be found in past threads here.