It's my understanding that there is not much left of Apion other than what Josephus wrote against him to defend Judaism against Apion's attacks, and that Apion is largely viewed in that context alone.
However it strikes me that if we consider that Christianity had not arisen during Apion's time, and that Apion was living at a time of great Epicurean activity, it would be logical to look to see if Apion was criticizing Judaism from what would amount to an Epicurean point of view rather than simply as a Stoic or as a generic believer in the Greco/Roman gods.
I gather for example that Apion criticized Judaism for being impious, and that sounds consistent with what Epicurus says about incorrect beliefs about the gods.
At this point I don't have anything more but I've downloaded Josephus "Against Apion" and see what i can find.