Step 05 - Connecting the seat and back support.

113) Go to the Spline subobject, select the hole spline and use the Outline tool like this:

114) Now apply an Extrude modifier to this shape.

115) You can alway back to the base of this object (Line) and edit it vertices and segments.

116) Next step is make a cylindrical rubber in this area.

117) So create a Cylinder primitive.

118) Reduce it Side parameter to 8 and Height Segments to 1. Now we have a low polygon objetc.

119) Convert this object do Editable Poly and delete this big face.