Blender custom models / Collider issues

I'm working on a dice tower for Tabletop Simulator. I don't know if this is a Blender question or TTS question. I still have a few planes to add on the inside, but the model looks good so far (I think) but the dice just sit on top, not falling through the center and out the front. I use the .obj file as the collider in TTS, so I don't know what else could be wrong. Any ideas?