Well my ventilation system is comprised of a computer fan to cool down the 35 watt cfl and i bought a fan with hepa filter/carbon filter and ionizer that pulls the air out and keeps negative pressure. The temperature changed from ~65F to ~75F when i added the 35W hps. I think if the temp increases too much when i will add the 70W hps, I will slip a piece of plexy glass between the lights and the box.

I hope this will suffice during flowering, which i plan to start in about a week. Since my 48" shoplight setup with fluoro tubes is in the flowering chamber as well as the seedling box, i plan to also have a 24 hour per day cfl in the seedling box to keep them from going into flowering. I think this will work but I would appreciate input from anyone with experience with this. My plants are currently on 7th internode and are about 7 inches high, and pretty girthy.