My background is Caravans and Motorhomes, so it's slightly different principals and surfaces. However, we've always been advocates of covers with our work, and I've used them on every Caravan I've owned for the last 15 years, and now on my Motorhome.
Although we recommend them on our jobs, we always give a couple of strict rules, and providing these simple rules are followed, you should have no issues at all, including the years of use with my own.
Rule 1. The vehicle being covered has to be perfectly clean, and dry before covering. Clean means exactly that. Zero dirt and dust on the exteriors surfaces. If you cover a Caravan or Motorhome dirty (very common issue) You will be left with whats known as 'Tiger stripping' in my industry. This is where the general dirt on the surfaces, and the natural movement of the covers in the wind, will mark the paintwork that only a machine polish will remove, hence what we do for a living. (We actually have a Blog post on my website that shows the damage caused by a cover, and after we've rectified this)
Rule 2. Make sure the cover fits properly. If it moves or flaps against the paintwork over a prolonged period because it doesn't fit correctly, you will know about it once uncovered. We often use several companies for our covers, including
Protec Covers - Pro-Tec Covers. Caravan Covers, Motorhome Covers and Tailored Covers for Vehicles Car Covers, Caravan Covers & Motorbike Covers from Specialised Covers and
Caravan Covers | Kampa
If it was myself and my T6 wasn't being used every day, i'd be buying a fitted cover, and would be confident through experience that if you follow the simple rules, there won't be any issues.
Here's mine as it stands right now. It's been under cover since July, and will stay there until February next year, as it does every year.