Your going to need to ventilate that air if using a MH and/or HPS especially a 600watt within that space... Oscillating fans wont do the trick, I would really recommend you getting a slightly high powered CMF fan (maybe at least 175 CMF), with ducting to ventilate the air out of there... Or at the least a regular fan that sucks the stale/hot air our of there to create negative pressure and get fresh/cool air in. Some how, someway, otherwise, I promise you, (And I mean this with the utmost respect, as I in no way mean to offend you) but, they will die of heat stress.. I have a 10K Lumens (not sure exactly what watt) but a high powered 4 ft 4 tubed T5 Floro set up, and my temps fluctuate from 60* F To 85*!!! Just from a High Powered Floro, imagine what it'll do with a 600 watt HPS or MH? Especially in the summer times. Do as you must, but ventilation is a must when using HID indoor, especially with no window you know? Good luck bro!