I covered my old 2003 Prowler with an Adco cover under trees and this was what it looked like after about 8 years.
I did replace it with another Adco and that one did well too. then I traded that old 2003 Prowler for $6500 in 2019 for my new 2019 Rockwood. They said the biggest selling point was that I had kept it covered in storage and it looked great and no leaks, no mold, no mildew.. The cover would be dry in a couple of hours after a heavy down pour.. We get a few of those in WA state..
Anyway, I have a new Adco cover for the Rockwood and it's been fine so far..
Sure, I can't open the slides with it on, but that's not a big deal for me.
Cover or not to cover... You'll get the horror stories on it and you'll get the good stories...
In the end, it's all up to you.. If your last Adco only lasted 18 months, what conditions was it in? High winds will rip it up for sure... I can see that.. I pulled too hard on the old one and it tore. I felt that after 8 years, it was time..
Good luck!
Mitch