Unfortunately this is the best I can do:
From all the sources I've read, it was exclusively applied to snorkels. If you wanna make a non-historically accurate skin, though, that's cool. As a note on color, the base rubber (BUNA) is black like the Oppanol that Alberich is made of, but it also had iron-oxide (rust) in the mix so it may have been some shade of red. The pic above seems to hint that it was not black. Oh, and the texture is quite three-dimensional, so it will require extensive bump mapping to be accurate.