Way back-
(RC 10th scale combat airplanes)
What ever foam gotten that was sized right-
Hot wire cut to wing shape then,
wrapped with brown paper bag, skinned so to say, regular white paper glue thinned down with water sprayed on with old hair bottle pump type, to glue down both sides, (foam side and outside).
After dry time an extra outer coat then sanded smooth.
After that a couple of coats of spray can clear coat
made for a pretty tuff wing skin.
white glue made seal coat to not let clearcoat solvents melt glue if done carefully and slowly letting coats flash off before adding more.
Of course they had spars and even extra strength from strips of plastic like from a banding machine but cut down to a smaller width but still inserted into a simple razor blade cut down the wing leading edge and pushed inside to be flush with edge. One more was glued to spar side to be 90 to the wing width before spar was inserted, used plastic same size as spar.
This plastic does not like to bend edge wise.
$0.02