loop a rubber band through the 2 holes in the rear.  Use something to prevent one side from being pulled back through that hole while you stretch the other side over the rear half of the rubber band ledge on the other side.  Slide that piece into the base.  Now do the same thing for the other side.  take the other end of the rubber band and loop it over the rubber band ledge of the other rear vertical bar and slide it into the base.  

Now we need to put the 2 front bars in and attach the rubber bands to the rear vertical bars.  gently slide one of the rear bars forward enough that you can loop a rubber band around the front half of the rubber band bar and gently slide it into the base, just until it is secure and wont slide off.  loop the other end of the rubber band on the front vertical bars rubber band ledge and slide it into place in the base.  Repeat for the other front vertical bar.