It is 100% supportable that the "box" represents the womb in Hesiod's version of the myth from his Theogony. In brief:
* In the Theogony, Hesiod never mentions any vessel save Pandora herself.
* Pandora is cast as the mother of the "race of women" who were created to vex men (i.e. they are the source of evil named by Hesiod in the Theogony.)
* In other versions of the myth, no "box" is mentioned, but instead a _pithou_ meaning "jar" for wine or oil. (If wine, it could represent blood, and oil is a lubricant.)
* The idea of woman as vessel is a major point in Apollo's notorious arguments in Orestes' defense in The Eumenides, demonstrating the existence of this concept in Ancient Greek thought.
You can find a more detailed explanation of this element of the myth here, as well as a discussion of the possible meaning in Aesop and Hesiod.