Belly Movement...

I struggled for a while with how to weight the belly. Surfaces so far away from bones tend to wrinkle up during deformation. After trying several variations of the deformation mesh, I ended up using a couple of lattices front and back with weighted hooks to the bones of the spine. Here you can see the lattices, hook empties, and the resulting deformation with the belly pointing downward. Both the front and back lattice use the same set of hooks.