I have seen a rear bumper like that on a friend's Vanagon.  My father made one
out of 4" steel tubing for our '84 Vanagon GL.  Just welded caps on the ends
and then mounted it to the stock bumper brackets.  Spray painted black and
looks sweet.  No more rear bumper crumples and I could weld a bracket for
towing on it if I wanted.I offered to make some more of these a while back but
really didn't get any responses.
Ken Wilford
Van-Again
John 3:16