I have an oscilating fan running at its max & with the door open it does alright. I have read on hear where folk feeze 2 litre bottles of water and stick that in the room but thats a fair bit of work. One of the reasons I went 18/6 instead of 24 hour was to keep the time the door is shut with the light on as short as possible. So at the moment they get pretty hot between dusk till midnight & then again from 6am until 8am when I get up and open the door. If you have a fan blowing cold air from your AC into the closet during the day it might take longer to heat up when you shut the door.

However I have also read around here that to use Co2 you need high temps so I am going to do some searching and see if it would be a bonus to increase the C02 in the closet while the door is shut and what schedule etc.. Might be able to turn a PITA into a benefit.