i dunno my 250w hps in a 4x4x8 closet still put off temps around 78-81 which isnt that bad, but i didnrt really have much of an exhaust. I am currently using the 250w hps in a 21"x18"x56" space with a 4.5" cpu cooling fan, and my temps get aroun 79-81. So i think you should be fine considering space difference. Jus us a couple oscilating fans and I bet youll be fine.

Also.. is your electrical included in your rent?