Grow box plan help

Ok so I plan to make a grow box using 6 2 x 4's with a 400w hps lamp but my problem is i dont really know how to install the carbon filter, like do i still need the exhaust and inline fan or what? please help...

When i make a cab i like to use 2x2's instead of 4x4 cause their cheaper and not as heavy makes easier to move around and what not.yea you still need a fan and exhaust,how else you gonna pull air through the filter?theres alotta ways to set it up,but basically you want your inline fan to pull the air out of your cab so fresh air will be sucked into it.if your useing air cooled hood you may want to put a filter before it so you aint sucking dust and stuff into it.or put before your exhaust fan so it pulls the air through it.you want the fan to do more pulling than pushing..hope this helps.