[Stefan-A]

It would make sense to me not to brumate tropical species the same way. The way to brumate them appears (I'm trying to do a bit of research as I write this) to be to shorten the light period and lower the night temperature.

I don't know if it's how it works with indonesian garters, but it would make sense to me to apply the same methods to them. If nobody else can tell you the correct way to brumate them, my suggestion is to use the same methods that are used with other tropical snakes, for example ball pythons.