Covers are one of the big debates on each of the trailer forums that I frequent. Ask 10 people if they cover and half say yes and half say no.
In full disclosure, I would store in a barn if I had easy access to one, so I use an ADCO cover.
Here's my take on the debate.
Those who use a cover typically say that it needs to be a good fitted cover that will breathe. The two keys are "fitted" and "breathe". Fitted covers will reduce or eliminate the problem with wind blowing the cover and causing the finish to rub off in areas. Breatheability is important to let the moisture out.
The nice thing about these covers is that you have a clean trailer when Spring comes around.
ADCO is a popular but expensive brand of cover. CalMark is a very good and very pricey brand.
Whatever you do, do not use a plastic tarp! A plastic tarp does not breathe effectively and may cause mildew and mold. Many people have reported rubbing issues on their trailer; especially if you are in a windy area.
Now, for those who don't believe in the covers.
Those who have used a cover and don't any more say that the cover was a PITA to install and take off and sometimes ripped or broke off pieces of their trailer like the rain spouts. We use tennis balls on our downspouts. Easy on and off and no tears.
They will say that a trailer is meant to be outside and they typically point to the trailers sitting all winter on the dealer's lot as proof. Take that for what it is. Dealer's store outside because the alternative is expensive. They would store indoors if possible.
More importantly, these campers say that cold, snow and rain should not cause problems if, and this is important, we do a good job cleaning and maintaining the roof. Every time you clean the roof you need to inspect the sealants around all of the openings and the seams on the roof. You need to thoroughly inspect the roof sealants for potential leaks and reseal any areas of the seams and around openings where you suspect a leak. It also helps to tilt your trailer so that water can drain off as much as possible and not pool any more than necessary.
So, there's no right answer. Actually, the right answer would be to store in a covered area, but not everyone can do that so you can choose to cover or not. Just take the proper precautions with either method and you'll be fine.
DW, 3 Kids and our Goldens
2012 Shamrock 233S
2008 Toyota Sequoia 5.7L 4WD