COVER?

I've used a cover since new and my TT looks as good as the day we brought it home. The cover is not going to act like sand paper - sorry but that just doesn't happen - it's a great theory but not real life. The only time I would advise against one is if you live in an area that gets a lot of wind storms. They can be torn up by those but otherwise hold up well - or at least our 9 y/o ADCO has (which is filthy BTW).
The more you can keep the elements off your RV the longer it will last.