I would suggest using a simpler, solid state thermal swtich --
This is a N.O. 45-C solid state:
http://www.ebay.com/itm/180861327881?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
Also, here's a fan that would probably do the job nicely! Its thin, wider then most standard PC power supply...