If it was me, I would be concerned with ventilation first. Your going to need cool fresh air coming in, hot air exhausted out. Mylar reflects heat as well as light, and 600 watters get hot.

Turn your lights for about 12 hours and check the temperatures/humidity. I use a digital thermometer, that records both and the highs/lows. You need to stay below 85 degrees and above 70.

Good luck with your grow.