Ahhh, the future is plastics, at least for this one from February of 1942.
But Walker then re-used this concept repeatedly in 1943 and 1944 for Bohn where it exemplified where aluminum would be used for automobile bodies.
All of his streamlined bubbletops from this era seemed to be rear-engined, direct drive hydraulic coupling, etc. etc. that influenced Preston Tucker so much that Walker's design was cited as prior art in the patent for the Tucker automobile half a decade later. Here's Walker's patent, included as a reference in Tucker's patent, that was used in Bohn's ad: