I don't cool mine at all. What I do is put the room lights on a timer to stimulate the season I want them to think it is.
People that are in the north that have natural lighting coming in through their windows don't need to do that, however down south where there is not much difference in daytime lengths, from one season to the next, may need to do this and black out any natrual lighting that comes in.
I use this method for a couple of reasons, first my main leo room has no windows, secondly I can breed using two seasons so that half the girls start in Feb and the other half in Oct. It can also help females that are not up to the size I want them to not ovulate.
I have had various reptiles throughout my life and most have brumated themselves. Up here in New England they just seem to sense the season changes, even the ones that were kept in rooms with no natural light.