I used to have a 3x2 turtle table I built a top for and kept GUs in when they were young. I've since scrapped it and keep them outside most of the time. The last couple winters have been unusually cold and I've brought them inside but they just hibernate under a couch. This is the only picture I could find of the old turtle table. It was originally for my M. emys emys that spent their first few winters indoors, they're now outside year round also. Half of the lid was off for this photo but it was just a couple 1x4 frames with hardware cloth stapled/bracketed on and some hook locks on the sides to keep them secure. I stapled vinyl to the sides/bottom and sealed the cracks with silicon to keep it leak resistant.