fresh air is crucial to plant health. I would have a carbon filter and suck air through it, then out into some other area of the house (many room s have return vents, use that!). Then, unless ur space is absolutely air tight, air will get pulled in through whatever openings there are (or you can force it in with a fan). Then you shouldnt have to worry about the odor leaking out, because air will be coming in through any cracks or small openings in the box, not out.