Maybe some plaster over chicken wire and then cloth and resin? Wouldn't want a featherwgt. Airscream to lift off on those expansion seams. Which brings me around to the two Airstreams that Jim and Corky and I "inspected" at Burnt Cabins PA. The smaller which I believe was a 19 Bambi had puckers between the rivets in the belly seam at right rear. As these curved plates and the tooling for them is carefully lofted, this excess length in the edge of the overlapping panel is a little pointer to a lack of quality control way upstream of final assembly. The larger of the two had an applied belly band over that particular seam.
I guess this tiny apercu is on topic? Or not.