That sounds like a 29 gallon tank. That size is great for cresties, I housed up to two females in mine.

Remember that if you get two you will have to make sure they are both females, and not male/female, or male/male.

Be prepared though, even some females can have territorial issues.
So you may need to end up separating them at some point.

But yes that will work for crested geckos!