I keep my spencers in outdoor enclosures (Brisbane coast so warm enough). I always give them a foot at least of sand loam for digging. and then over that in a big heap, a bale of straw or two. They will always dig a burrow under the straw for nighttime and for winter retreat. Underneath the sand is squaremesh that runs at least a foot in from the sides of the pit so they won't dig their way out. I used to give them a hotspot light for the cooler months but frankly, I turned it off one summer and never turned it back on and they do fine anyway. From May to September, they spend most of their time in the burrow, only emerging on bright warm days for an hour or two and they aren't fed then either. The southern end of the cages is covered, either in plastic sheeting or colourbond to protect them from the storms and rain and the burrow is protected from flooding that way. I have racks built so they can get up on them and see whats happening around them and sunbath, they love that. They always have access to a large tub of water and enjoy bathing in it as well. They are a very simple goanna to keep, not aggressive and pretty calm. Excellent eaters too (of fingers or food, they don't discriminate when lunging at dinner).