If i were you i would get a bigger enclosure for him, one of those tubs but bigger is ok but a bookshelf on its back is even better.
But if can't get a new cage then... You need to get a different substrate called coco coir, or even just plain dirt. I would then bury the hut and put a large flat rock on top. I would also point the light forwards the rock and move the light to where it pints straight down and move the food and water to the other side.
He needs a much larger enclosure. That box is too small for a hatchling, let alone an adult. The stores should still have on sale, the very large plastic tote boxes they sell for fake Christmas trees to be stored in. If you can at least get one of those. If not, get two of the larges tote boxes available and attach them together with a tunnel or cut out between them so he can have the room of both. The substrate needs to be replaced with the items mentioned above. The water dish needs to be shallower and buried level with the substrate. The plastic or clay saucers they sell to go under clay flower pots work good for this. Be sure it's big enough that his whole body fits in. It does t have to be too deep though. Then a couple edible or fake plants would be nice too. Take a look in our enclosure section. You should get some good ideas there. If you have the room, even a plastic kiddie pool works good.
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When aquariums and plastic totes are 'measured,' they include the tall sides. So "40 gallons" really isn't all that big when you consider a tortoise needs floor space, not tall sides. Buy another tote exactly like the one you're using and cut out opposing ends, then set them together to make one big tote.
Quite a few folks here on the Forum use coco coir (Bed-A-Beast) mixed with either top soil or some other medium. I really like the fine grade of orchid bark.
Once you've made the habitat bigger, you can move your hiding place over to one corner, then add some driftwood or a couple big river rocks, maybe some plastic plants. There are all kinds of things you can put in there to make it more interesting for him. You can even pile up the substrate over the hiding place to make it like a cave.
Honestly, to me it looks small and bare. Make it bigger if you can and add some plants and rocks to break up the landscape a bit. There are a lot of good example of indoor habitats in the Enclosure section that you could get some ideas from.