On a previous setup where vertical space was at a premium, I had my fan and filter outside the tent. It will work, but as everyone has said it's not ideal. I rolled up the prefilter and put it in the center of the filter so that it would collect any large particles that might get sucked in. The key is having a large enough fan with a speed controller when you are pushing air through. Too fast and it won't remove odor completely and too slow & you'll lose negative pressure in the tent. But unless there's a good reason not to, attaching the fan to the filter and hanging it above the lights is the way to go.