yeah, i have the same setup with a 250hps, wish i had the 400. what i did was put an intake pc shooting air at the level of the plants. it pulls air in from a hole cut into the area between the stud in the drywall. along the same stud space i drilled a hole on the other side of the wall (MY BEDROOM) and fit a wall vent over so it is not suspicious at all. that is my intake if it makes sense.
outtake i rewired my bathroom fan to a new one that i put in the top of the closet. it pulls air through a carbon filter and exhaust through a hole i cut into the ceiling. with the way i wired it is hooked up to the switch that controls my bathroom fan.
i love this system. before i used to just have a closet in another room and just kept the door open with a fan on. now, i have the closet shut with even a blanket over it to hide the door. temps are not a problem at all and i also get constant air exchange