USMC Vet, I had the same concern and checked out a local Transit about this. Surprisingly the seats are inboard enough that it would be difficult to get a trucker's tan with an elbow out the window. Each door in fact has an ample arm rest below the window opening, which fit me quite well. The new episodes of American Pickers on the History Channel have a new Transit in them, and it is easy to see Frank and Mike with their arms comfortably on the the arm rests while cruising down the road.
Now, if they could get those huge front fixed panels in the doors to swivel open like the old wing vents. I read someplace that this would be an option down the road, but not sure where I saw it.