Do you have an intake fan? If so where does it come from your house or outside? I have a top of the line grow and I have absolutley no heat problems. Do you have wall mounted fans?
1.) put the cab in a room with a lower ambient temp. 2.) if you have a fan (on the top) pulling air out of the box, increase the number of passive intakes from the bottom of the box. you have some already, right? what type of light set-up are you using? a vented hood reeeeeeally helps with lowering temps.
i have an intake fan and a fan behind it to bring in fresh air from out doors. it is all inside and it is on the 3rd florr or attic of the house . i have a 5 gallon bucket in front of the fan now and my humidity is leveling around 47% rh. my temp whent to 78 degrees with the doors and windows open but i would like it to about 72 to 74 to prevent heat stress and dwarfing or hermafiditing of my female pre flowers. i am using 200 watts of warm white cfl and could add more but my box is 4'x2'x2' and it seems to illuminate it just fine if not too much. if there are and bugs in my system please let me know.