I grow with a homebox XS now as well. I have a 4" small duct going to the bottom for intake and then i vent out with with the back wall carbonfilter 4" to a reducer of 3" out to the 4" fan exhaust. no need to have 2 fans! putting fans in will cancel them selves out and you wont have a negative air effect in your tent which helps with airflow. Good Luck! check out some of my old posts. you can see the tent.