Thanks for all the input... I'm putting all together at the moment, and ventilation is definitely going to be an issue, the last thing I need to be doing is making brownies in my cab.

I'm thinking about you suggestions and I'm going to try to incorporate all of them:

1)I'm gonna cut 4" hole at the top, use a 4" 90 degree bend into a 1' section that goes into a 180 degree bend and add a homemade carbon filter, filtering the exhaust and stopping light leak. I'm going to put the same thing at the bottom without the carbon filter for intake, creating a negative pressure effect. This is going in my garage so I'm not worried so much about neighbors....

2) try different mock setups for the lights including Red's idea for seperating this into two different chambers.

3) I'm caulking the seams of this cab to eliminate any possible light/air leaks.

4) I'm going to put an oscillating fan inside to help with heat and move the plants around a little to strengthen the stems as suggested. If I can, I'm going to put a smaller one to cool the "light board".

Let me get back to the garage and finish putting this together