The quality cover we bought was made by ADCO and advertised as "breathable". Last year in our Winnie's first time in winter storage, we put the cover on and it performed well. No ill effects at all from wind or snow. No abrasions on the coach finish. No damage to antennas, vent covers, or skylight. The only difficulty in removing it in spring was that there was some snow on it, so we had to take our time to remove the snow first then carefully ensure it wasn't snagged on anything or still frozen to the roof. The only significant problem was a couple of the tiedown strap tails were frozen into ice under the rig. Had to cut them to get the cover off. This year we got a storage spot in a paved lot with good drainage, but the spaces are a bit on the narrow side which would have complicated getting the cover on, so we decided to forgo it this winter. It also occurred to us that since the rig was a rental before we bought it, it had survived at least two winters quite nicely uncovered and still looked perfect when we got it, so why cover it now? Now if we were in the sunny south instead of Alaska, I wouldn't hesitate to use the cover. There is much more potential of damage from the sun that from snow and ice.
2016 Minnie Winnie 27Q on a 2015 Ford E450 chassis. Retired U.S. Air Force. Living in Anchorage, Alaska