This is a picture of our brumation last year. We put the adults in plastic boxes of 40cm X 50cm and young garters in smaller boxes. In the boxes we put wood thing (don't know the name ) and dried leaves. We make it very moist, well not soaking of course !! We don't put a waterbowl in.
Then we put the boxes in the space below our house (crawlspace ??)

This works perfect for our garters and we'll do it the same way anytime soon now