Plastics and Wooden Parts in German Aircraft
Now I have found references to various chemical sealers. One was called "polystal." Its composition was a poly-di-isocyanate resin made by the I.G. Farbenindustrie. It was used for sealing integral wing fuel tanks. Now this was for an all wood wing which was itself bonded together with "Kaurit-W" whose chemical mixture is not described in that report. "Kaurit-WHK" is also mentioned as a bonding agent. It may be a variant mixture of Kaurit-W.
Now the word "stealth" was not used but two reports were issued concerning German work on "radar camouflage." Doing this type of research usually involves years. There were other technical intelligence teams in the field which produced reports: F.I.A.T. or Field Intelligence Agency, Technical:
http://digitalcommons.unl.edu/libelecrefmat/6/
The American Counter-Intelligence Corps worked with T-Force but a complete history of the CIC has not been published.
So, answers do not come quickly and diligent research that is totally unbiased must be the standard operating method.
Ed