A basic dirt/sand nest is always mixed with some natural clay, as to strengthen tunnels and prevent collapse. The next concern is hydration, and for that I would recommend a bottom to top hydration system. A simple way is just to use a cut straw piece that reaches all the way down with a cotton ball on both ends (to prevent them from entering it) and a cotton ball on top. Then hydrate by taking the cotton off the top and replacing it when done.
That suggestion is garbage however compared to the incredible research and work that dspdrew has put into his formucarium research. Check out his topics on them if you want some of the best.
Edited by Shaye, August 22 2017 - 10:30 PM.