My recommendation is cypress mulch, it's safe for snakes, keeps moisture very well (even has visual cues when it gets dry), keeps heat well, doesn't break down easily, it's dirt cheap, and you can find it nearly anywhere in large sizes.


http://www.lowes.com/pd_92889-76450-...lch&facetInfo=

3 cubic feet will do about 8-10 41Qt tubs so expect to be able to keep this stuff around for a while.