License plates are p***enger car not commercial . So it's got to be a motorhome or coach of some sort.
Looks like it has furnace heat vents...and the generator vent door behind the rear fender....I like that 'port hole' effect...sweet!
Here's a screenshot of the CraigsList ad (the ad has been pulled): Those headlights look like sealed-beam conversions to me. I think that the truck is 1939 or older.
That's a neat find. Can you tell if the porthole and oval windows are original or were they possibly added later? It could be an old retired moving van that someone added some style to. Post the pics up over on hankstruckforum and you may get some more info.
If it was military, there would be OD paint under everything, and it likely would not have a stainless grill. The double rear doors do not look like it was originally built as an RV. It does not surprise me if someone diverted to for RV use later. Most of the Civil Defense vehicles were post WWII, weren't they? This truck is prewar. It could have served as a mobile command unit. Maybe it was painted red to match apparatus, but my guess if that it was a commercial van.
My thoughts too (or Sturgis bike hauler). I'd chrome the bumpers and wheels, lower it a couple inches and go two or three tone on the paint. Maybe black over dark maroon or Washington blue (can I get a photoshop?). You could utilize the 'swoosh' between the side trim (possibly chrome plate the trim) as a canvas for a shop name and since it "flows out of" the side windows, I'd consider painting that panel black and limo tinting the door gl*** to match. As much as I like vintage power plants, I'd drop in a ***mins turbo Diesel. Possibly find a wrecked late model dually or Motorhome and use the entire drivetrain or possibly the entire RV ch***is Tanks, inverter, generator, etc). Back would be built race trailer style shop/RV with a laminate floor. Fold down couch/bed or possibly a fold down upper bunk behind he drivers door along the upper window. Small kitchenette. Old school utilitarian stall shower with ****ter to save space. Plenty of room for a tool chest, small 110 MIG, overhead cabinets, flat screen TV, stereo, etc.
That is cool on so many different levels. All you need is a 60's g***er and a trailer and make that your work shop.
I keep thinking "amboolance man, amboolance" like cheech & chong. Like post WWII. All I found for post war was this Ffffford. The 1937 & 1938 grilles were vertical in the center, with horizontal bars on each side. From 1939 thru 1947, the vertical bars were gone and the grille was all horizontal, which is what the OP has. I found one record saying that GMC had sold 171 van-bodied units to the military in1939. All I got.