you can grow at 85 or above, you can also repair a leaking radiator line with duct tape. i consider above 80 too hot, yes the plants will live but the quality and yeild will be no comparison with plants grown in the low to mid 70's. with 350watts of cfl you should be able to take care of the heat easily. my 2' x 2' x 3' cab has 350cfl as well. i have a 180cfm fan and that keeps the grow at exactly the same temp as the house. the air doesn't have time to heat up even 1 degree, i could probably have a 1000hps in there without raising the temp! the trick is to replace all the air in the cab as quickly as possible so it doesn't get a chance to heat up. blowing the air around with fans does nothing to get rid of the heat, you have to get it outta there fast! the doorknob idea was a good one. thanks garden knowm. i would use this fan vented through the doorknob if it was me:
http://www.plantlightinghydroponics....roducts_id=351
you might need a reducer but it shouldn't cause too much back pressure.
good luck