Did they ever come with any and has anyone actually added them? While at Hershey I picked up one but found out it was for a car. Might find another dash and see what I can do.
The 1937 Sales Handbook for Commercial Cars and Trucks Accessories section, page 132, only shows a heater. The photo appears to show only a heater with a vent.
With a '37 or '38 truck, if the windshield fogs up you just crack the windshield open. You don't need a defroster. You would really have to alter the dash to make room for add on defroster ducts. There just isn't the room like the later dashes. Kent