Mine's in a 20G long tank, but he sits in one corner burrowed down all the time. I've got about 3 inches of compost dirt mixed with coconut fiber covered in moss. His usual spot is underneath the big clump of moss in the background. (For this pic I had enticed him out with an earthworm and he's all puffed up from being disturbed with camera and lights.)

It's actually pretty funny when I release crickets in his cage I just see the clump of moss moving up and down as he gobbles em up.