I prefer to cover. It protects the finish from the elements. Sun exposure is quite damaging to the finish and plastics. I haven't had any problems with chafing or mold as others will warn you about. I would recommend that if you do purchase a cover that you buy one made of sunbrella fabric. It will last many times that of a tyvek cover in my experience. I'm on my 5th year with a sunbrella cover and it looks like new yet, my tyvek cover on a prior RV was in tatters in a couple of years. Also, consider a cover with zippered access doors so you can conveniently check on the interior from time to time while it's in storage.
Al