yup that temperature is fine. a 20 gallon is a bit big but you can make it work. use paper towels as substrate and watch to make sure that the crested is finding its food. you can "show" it where its dish of crested gecko diet is and hand feed it to get it used to being handled. if you feed crickets just watch to make sure that the gecko is actually getting them.

also take a look at the crested caresheet if you haven't already: http://www.ball-pythons.net/modules....ewarticle&id=6.