I have mine covered all winter. Never had a problem with scratching. I do wash the trailer before storage. I think a lot has to do with whatever you are using as a cover. I have an Adco cover on mine. It's made of a tyvek type material.
I would think the quality of fit and material would be a priority. If any part of it flaps in the wind, it will mark the camper and probably west out the cover in that spot. I’ve never bought one or looked into them so I don’t know a good one from a crap one. I would prefer a pole shed with closed in ceiling so the birds can’t 💩on it.
2021 Durango Half-Ton D250RES[br]2013 Sierra 2500HD Duramax
Before I built a pole barn I used a cover. It did cause some slight abrasion where it rubbed on the corners caused by the wind. If you clean it before covering, the abrasion should not be a problem compared to the sun and weather damage. Do everything you can to keep the trailer protected, contrary to popular belief they deteriorate in many ways. Paint chaulks, plastic cracks, vinyl shrinks, rubber cracks, caulk hardens, joints leak, frames rust, decals curl and things yellow.