I've got a cab with two chambers that are 2 sq ft each. Each chamber has 6 x 42w CFLs. What I did was mount an 1/8th inch piece of glass about an inch or so under the lights and put a separate exhaust fan on the light room:
That way, there's one 120mm computer fan extracting air from the plant rooms and then one 120mm for each of two glassed-in light boxes.
My cab temps drop down to the high sixties at night (68 F) and approach the low eighties (82 F) during the day. If I noticed the heat creeping up, I can spin the fans up higher. They're currently all operating at about 33% of max which is much quieter and keeps temps in line just fine.
I did like you did and took my plans to home depot and had them do the cuts for me.
Here's my box in operation:
keeping it simple is all i did and its all your doing and the plants are luving it.. growing weed is sometimes to easy
key now is not to cut before its time.. right around now is when you will see triches/hairs start to turn and they will/should start to popcorn out and swell like the one plant is doing and the other is not that far behind..id give it 4 weeks from here but keep doing what ur doing checking them triches. 
