After Otto Binder, the most prolific correspondent of SF fan Jack Darrow (real name Clifford Kornoelje) was their mutual friend, Bill Dellenback. In 1935, the three friends drove from Chicago to NYC, to meet up with various SF fans, editors and publishers.
In looking through some early Worldcon program books earlier today, I came across these ads taken out for the Thrilling science fiction pulp line. The Chicon 1940 one is by Hans Wesso; the Denvention 1941 one is by Virgil Finlay. Leo Margulies