I was using a tarp for the last few years. I did get some minor marking on the sides of the trailer from rope knots rubbing, but nothing major.
Did have a bad wind storm earlier this year and it caused the tarp to slap a side window hard enough to crack it... The packing tape is starting to peel, I need to replace that window.
In 5 years of ownership, I honestly don't think the tarp/cover has gained me much other than making the vent covers last longer. I spent 26mo living in the trailer, so it didn't get covered then, and it didn't get covered if there was ever a chance that we were going to go camping, so it was only covered for 3 winters, and uncovered for the rest of the time. My graphics still look great. I just cover the tires now, and hose it off before we head out.