some polygonal modelers like 3dsmax have a shell modifier ( with precision & efficiancy )

you can export a nurbs model with impossible shell ( thru OBJ ) and import for example in max ( c4d or blender ?? ... don't know them )

Max will show you holes on the surface of the shell if the nurbs model has not perfectly joined surfaces

if the shell is correct ... reimport in the nurbs software et voilà