I think you will find that, as built, your filter is going to create a significant amount of back-pressure. About all the home-built filters base the design on 2 cylindrical screens, sandwiching the carbon between them, creating a layer only a couple inches thick. This makes for a large surface area, decreasing the air velocity and allowing for more effective filtering. I imagine the air will be mostly trying to escape through maybe 2-3 inches of carbon closest to the inlet with this design, the rest of the carbon won't even make contact with the air your wanting to filter. If you are able to make it work, it will probably lose effectiveness pretty quickly, because of the air not being able to reach all of the carbon and due to the higher velocity of the air through the carbon that it can reach.