I tried not to glass the corrugation area or at least to use the least possible amount of epoxy. Then I immediately wiped as much epoxy as possible with clean kitchen paper. By doing that the glass fabric detached from the balsa filler that was used to smoothen the corrugations. The next day that epoxy had fully cured I cut the glass fabric over each single corrugation and sand the edges around the cut with sand paper. Wherever needed I used balsa filler once again to smoothen even more the corrugation.

Here are some more photos.

Stelios