Scratches? My daily commute on the Caltrain quickly cured me of this concern. The bike racks on the Caltrain are simple and effective IMO, but essentially just cram bikes together with elastic straps.

It’s a great way to unblock lots of people to utilize trains that wouldn’t otherwise. 2 or 3 cars of the train are devoted to bikes. That certainly is indicative of the environment and the temperate California weather, but still. Makes for a marvelous multimodal commute for me.