A dirty fabric cover can do the same.
For the first few years of her life, my Duchess lived outside during the driving season. I had an Evolution3 car cover; at the time, probably the best all-weather cover on the market. It got dirty. Nothing you could see, but it magically transformed into sandpaper. Thankfully, no harm to the gel coat at all. But the cover wore the chrome off off the top-most surfaces of the grill shell and headlamp buckets.
I call it patina now. 😎
As far as the trailer incident, you should never cover a vehicle while it is being trailered.
As happened to Kall, the constant buffeting (and I don’t mean Jimmy!) has a high likelihood of damaging the finish.
In addition, no matter how well you secure it, you run the risk of having the cover blow off, and on to someone’s windshield. That would not be a good thing.
Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster
If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)