ZacD, The cracks are a little too deep but more importantly they angle out too much. Your crack profile looks like a V, it should look more like a ||, much less open cracks.
@ZacD: Everything you need to know is here: http://forums.sc2mapster.com/development/artist-tavern/9662-article-modelling-and-exporting-for-star-craft2/ Really not too complex, but keep in mind this tutorial doesn't get into the data editor. That's where the real headaches begin, luckily I haven't had to deal with it too…