I'm of the opinion that the cover only allows a minimum and with short days may not be enough. Whereas the smaller 15 watt panel and controller should be able to maintain one battery, perhaps a 30 watt set up would be better to leave on over the winter. On the other hand, leave the cover off and allow the 160 watt unit do it's job.
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Jim
Sometime life gets in the way of living.......
My suggestion of a small solar battery minder was for the owner who uses a cloth cover that precludes his roof-mount solar panel from getting enough sunlight to keep his on-board battery(ies) topped off. If you are storing indoors without 120V AC, I guess it would depend on whether your wire leads from the solar panel to the controller are long enough for whatever route you would have to string them. Our 21' is under a carport, and the roof-mount 160W solar panel still receives enough sunlight to keep our battery topped off - granted we live in Alabama, and the camper is parked so the rear of the camper where the solar panel is mounted is on the South end of the carport.