The model you refer to is the Canopy Express. It's essentially a 1 ton panel with the sides cut out. There's roll down covers for the sides when the wheather is bad. The primary users of these were truck farmers. The open sides allow the farmer to sell his produce right off the truck, and keep them protected from the elements better than just being on a table.
There's a local Chevy restorer who had one, his was a '46. I'm not sure if he still has it, but I have seen it in person. They're definetly different from the normal trucks.
