121) From the Subdivision Surface menu, enable Use NURMS Subdivision options and raise Interations parameter to 2. This will give you a subdivided model feedback in real time.
122) Go to Border Subobject and select the first border. Active the Scale Tool and hold the Shift key from your keybord, than click and drag X and Y axis at the same time. This will create new polygons and we're starting to shape our rubber.
123) Now with Select and Move Tool, hold down shit key againd and move the border in Z axis creating a kind of border.
124) Use the same tecnique of Scale Tool with shift key in the botton border.
125) If you wish, go to other Subobjects and re-shape it.