Some good ideas. I'm curious what color the bike is. White or Black. I also guess there is a little space there and even when the bags are mounted, there is a certain amount of vibration.
So, here are my thoughts. Even if you use the soft side of the velcro, there could be some abrasion to whatever surface is rubbing against it. I'm taking into consideration that it will trap dirt and eventually scuff the piece rubbing against it. Using both pieces stuck to both sides would help prevent that.
With regard to using rubber: Lets say that the bags are black or your concern is greater than looks, which by the way, would likely not be impacted. If it were me, I would get a roll of double sided tape from the hardware store. Gorilla Tape would work good for this. It is just a little thicker than scotch tape but sticks amazingly well. With the bags in their correct mounting location, use masking tape to locate the spots on the bag where you want some abrasion resistance. Inside those 4 rectangles, attach the Gorilla tape and attach a strip of old inner tube to that. Be sure to allow enough width of the rubber strips to allow for the small bit of movement that you are [evidently] concerned with.
Just remember that whatever you put there, there is a high probability dirt will get into the space as well. Just take that into consideration.
John Henry
