If the tape doesn't work or doesn't appeal, you may need to look into a new seat bag. I replaced my falling apart little Cannondale bag with one of the newer Detours bags that the LBS guy said they liked because no velcro = no rubbing....but the shape seems to be wrong and I am getting some rubbing.
Not enough to abrade the fabric (yet) but I'm going to do an experiment with the old bag and the new on my trainer to see what the difference is and then take my bike with me to the shop to pick out a new one. Good luck!
Sit bones = ~135 mm, saddles that work ~ 155cm/6.1 in wide
2003 da Vinci (custom road/all-rounder)/Terry Butterfly Ti
1994 Gary Fisher Nirvana (vintage MTB/commuter)/Terry Butterfly Chromoly
1991 Terry Symmetry (NOS frame/fork, project in progress)
1973 Raleigh Super Course (project in progress)