That would be alot of heat. If you had the ballast on the outside of the box and ran wires into it that would help to reduce your heat and I believe would remove the "fire hazard" risk.

Get a small fan and mount it on one side of the box like an exhaust fan on the topside of one side and bore out a nice size hole on the other lower side. That would definately help!

Good luck with the grow!:thumbsup: