If you can afford it, stow it indoors. That will preserve it best.
Next is outdoors with a cover.
Leaving it exposed to the elements (especially freeze/thaw cycles) will allow the most winter damage.
Because I need to use my barn/shop, the trailer stays outside, under a cover for the winter.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!