Dynamesh is a great re-meshing tool added to ZBrush 4R2. You can use Dynamesh to hollow a model for 3d printing in a few steps. Without making a separate low-detail mesh to fit on the inside.
1.Set your mesh to the highest Sub-D level. Delete all lower Sub-D levels.
2.Adjust your Dynamesh options to smoothing: "0" and "1024" resolution.Click the Dynamesh button to re-mesh your model.
3.Hold the (Alt)key while inserting a cylinder into the mesh with the insert cylinder brush. Put the cylinder where you would like a hole in the model.
4.Select a thickness with the slider under the Dynamesh button. Make sure the Dynamesh options are set to smoothing "0" and "1024" resolution.
5.Clear all masking.
6.Click the "Create shell" button and wait. Dynamesh takes a few minutes depending on the complexity of the model.
This removes the (Alt) inserted cylinder leaving a hole in its place while hollowing the mesh at the same time. Click Undo if it the walls appear too thin or too thick and try again. Be patient it takes a few tries at different thicknesses to get it just right for each model. If your model has thin parts such as legs, arms and neck. I would recommend a thickness setting that keeps those parts solid for rigidity.