Here is an outgoing Canal Zone cover with United Fruit Company Almirante Panama corner card addressed to the Boston Mass office endorsed "company mail"
It has been marked with CusCR 02 dated Feb 6 1943 signed by examiner Staples at Cristobal. The reverse shows a CUsNO 01 marking (New Orleans) dated Feb 17, 1943 signed by examiner (Shelley?). This reflects a transit of 11 days via sea between the Canal Zone and New Orleans.
Dann Mayo's special study on Travelers' Censorship in the US During WWII notes that by the end of April 1943, " The Chief Postal Censor has also been in communication with the territorial stations and arrangements were being made in Hawaii, Puerto Rico and the Canal Zone to set up Travelers’ Censorship Units there..." making this an early example of customs examination of traveller's communications.