I met Jim last week, and me being a C15TA owner this subject came up in our discussion.
Have found these images in the thread
C15TA CES list and drawings - see items "11" and "19".
If anyone has ever seen the "Waterproof Blanket Case" or has any more info, I would be very grateful.
Jim mentioned he thinks they were made of rubberized canvas, hence being waterproof. I reckon this is an item that was used on other vehicles than the C15TA alone?