A trim wedge for your rudder.  Material is resistant to acetone, paint thiners and fuels.  Proseal would be a good adhesive choice to use to bond the trim wedge.  The hollow versions are 40% lighter.  Based on what I have observed over the years, .300 is the typical aft thickness.  ( I personally use .275 inch. x 1 inch x 4.0 inch long but each aircraft is different. )  To resist UV rays, a coating of UV resistant enamel paint can be applied.  
 
Note: the angled version is for RV's with a fwd angled rudder trailing edge.  if you are applying the rudder wedge to a Glastar or similar with a aft angle rudder trailing edge, choose the opposite side (left/right) orientation to have the proper angle orientation.