"Convex Collider" box causing crash

First time putting my own art into Unity so I bet that's what's causing it. When I load in my model, it's fine. When I add a mesh collider, it's fine. When I click "is convex" because I want it to be a trigger, it's not fine, and unity completely freezes. This only happens with the one I actually need to be convex, the other imported assets are fine, yay for me.![alt text][1]

Image Description: this is what it looks like when it's frozen. As you can see the "convex" box on the right has been checked but it hasn't actually been activated, and it's in the middle of crashing, but it never actually does. [1]: /storage/temp/126634-screenshot-18.png

Edit: I'm wondering if it's because I didn't clean up the vertices enough and there's just too many of them to handle all at once, so unity just sort of gives up...?The model is 16MB in size, which I was surprised by.