I'm having an issue with the solidify modifier. First off, all of my bodies are manifold so I've already been through that drill. However, every time I use the solidify modifier it adds thickness to the model but it doesn't "fill-in" the model. It seems to leave a void gap between the outer layer and the inner layer (see attached images). Can someone explain to me how I create a model that is "filled-in" and why it does this? Trying to 3D print an alien.