Messieurs !
Enhancing ribs may be done with putty or even paint (see "Filling Gaps" and Ian from Doncaster etc. comments)
According to the method I mentioned for sheltering surfaces from putty via Tamiya tape you of course may use it to create / enhance
ribs under fabric or if there aren't some where they should be (ex: Roden's Fokker Dr. I 1/32).
But instead of using putty one may also use paint: take Humbrol enamel paint out of the unstirred can and dilute it not too much;
configurate the desired areas with Tamiya tape and paint the free surface where a rib / rib tape should be; you may redo this
2-3x.
This way I think one may create very fine surface detail that might be harder to achieve using putty.
viele Grüße, Gunther