Keep the tent sealed - You'll notice with your Co2 running, the more time you spend in your tent, the more light headed you get. You don't want that escaping into your house, so keep your tent sealed.

I use CFL's but my air flow is forced, and goes over my lamps to cool them off, and that in turn cools off the rest of my box, I'm at a steady 77 at night, and up to about 85 if the sun is also beating on my boxes (without the sun on my boxes its about 80 during the day)

My air is brought in from outside (its about 35 here) its forced in with a 6" fan, and I have a 6" oscillating fan blowing it around the lights. I use a home made CO2 source, which is near the base of my plants, and the Co2 goes down into the potted soil.

I think your issue is that you should be bringing in cooler air for your light, that will keep your radiant temps down. My exhaust does my entire cabinet, and Co2 is typically off during the periods of which I'm exhausting. Your setup is fine, and I like the idea of the halo over the light, but running 1/4" tubing directly to the planters would be fine too. I use 2 liter bottles, and they just sit at the base of the plants, the opening of the bottle just over the rim of the container, so the gas leaks out and into the soil.

I'm working on ordering some slow release yeast that will consume my sugars a little slower, this way I can setup proper tubing to my plants. Right now the Co2 needs to be swapped out every 4 days, but since I'm producing so little CO2 I have no need for a regulator or anything else with this setup. During final weeks of flowering some strains I will run up to 10 of these, but typically I just run 1 per cabinet.

Anyway, to address your one concern, yes, if you leave the top of the tent open, Co2 will leak out, but you'll also be exhausting it with your current setup. Not much you can do about that. Keep it up though