Sometimes natural settings can be harmful. We try to perfect the lifespan of any captive bred animal by using things that are safe.
Sand, just like in some settings for example, can get into the genital areas and also lead to compaction. This is just an example since I have seen it with leopard geckos and Fat Tails. Some might be lucky and live years without being affected, but there still is a chance.
Just keep that in mind about making a "natural" habitat for a captive bred animal. Animals in the wild most likey lives shorter lifes in thier natural habitat.
~~*~ Also, I would research or ask some experienced fat tail owners about housing a male and female together. I beleive with leopard geckos if you house a male and female together, the male always wants to mate making the female stressed---and if the female mates and lays constantly, she will surely die of exhaustion, maybe illnesses, or deficiencies.
Also, you just got this fat tail. I would wait to do anything until you fully know their care. I am not saying that you don't know their care. Just make sure before you go out and buy another.
Sincerely,
Ajax