Put your 4" exhaust on top with duct going to a 4x4 container of wood with an exhaust of a smaller diameter coming from your box to an unoccupied space or outside. Inside the box put an O3 generator, you can easily build one with a neon sign transformer and a couple jars for cheap. O3 kills odor better than anything and you never need to replace carbon or anything. Dont put it in your grow chamber O3 could damage your plant. Put the transformer on a timer and emperiment with what timing you need to controll your odor. You could also stuff the final exhaust with dryer sheets to give it some back pressure and as a final filter of some sort.