I used to put a piece of rubber drawer liner (comes in a roll) between my tank bag and the tank to keep it from getting scratched.

 

I did a 2500 mile trip with the Marsee bag. I did spot one light scratch on the clearcoat. It's not noticeable, in fact I'm not sure I could find it now. Some grain of something got between the bag and the tank. I think some 3M type contact film would be the way to go to protect the paint. The bag makes magnetic contact to the tank in a 2 1/4"x6 1/4" strip on either side of the console. The magnets are covered with a kind of neoprene material. Easy to inspect and keep clean. I think the trick to not hurting the paint is to lift the tank bag straight up when removing it and not sliding it on the tank. Next time I do a road trip, I think I'll get ahold of some kind of protective film. If I left the bag on the tank all the time, I'm sure it would scuff the paint.