Freezing exposed C41 negs is probably not really needed, but all the manufactures do recommend keeping them in a cool, dark storage area and only exposue to the light when your going to print, once the emulsion has been fixed, the 'aging' process pretty much stops and the damage that can occur is due to the bleaching properties of light, we have seen developed C41 negs be stored in a trunk of a car, and still not show any real effects of the heat, but have seen negs stored in an area where they were in constant exposure to light, and they have degraded(faded) in a very short time, that is why we had to replace our calibration negs about every two months as they would begin to fade after being exposed everyday for a few minutes to calibrate the print machine.