I was thinking of the same thing as arizona heat can get pretty bad during the summer. When I was in afghanistan we used some thing similar to this inside our vests.
http://steelevest.com/product/gel-ice-15-oz-thermo-strips-set-of-5-sa1145-5/
Dont think it would be to hard to make a thin vest or sew some pockets inside the coveralls to allow for some well placed packs like these