FWIW my old-style Paulchen, originally purchased in 1986, has these locking
C clamps.  I purchased it used in 1998.  The C clamps would work great, but
I have a Specialized M2 frame with large diameter tubing, too big for the
clamps.  It does not have the extra support that rests on the bumper.  My
rear wiper works fine with the rack mounted.

dave
www.251.org