As tacman7 said, you have too many plants, which was also my mistake when starting. My vote on yours would be 2 plants max. If they're still there, check some of the photos from my signature. This was my first attempt at growing, also in a big box. The dimensions on mine were 2' x 4' with max plant height of about 4'. I packed a 600w HID system in it with a sealed reflector, and had major ventilation built in as well. I used duct wrap for inside insulation. One other note, you should be pulling air out, which will pull cooler air in. I used 2 bathroom fans in the top of my box along with a 150 cfm fan that sounded like an airplane taking off when it went on. All of this was controlled by a CAP environmental controller.

Good luck! Post more questions as you get in to it more.

Peace,

Farmer Rich