Opinions on winter storage for a plastic kayak?
The options are a cold (Wisconsin) garage where it could be kept upright or a warm basement where it would have to be on its side or upside down. I don't have an indoor rack, but I'd be willing to consider using one.
paper or plastic?
Actually, plastic or fiberglass is the real question? Plus will they be sitting on a rack or saddles or just on the floor?
Plastic (roto-molded) boats are supposed to store well on their sides. Fiberglass boats on their bottoms.
Outside
The plastic will get stiffer, but ever so slightly more brittle as the temperature drops.
If you aren’t worried about running into it with the car on the one night that drops down to -15 F, then I would just leave it in the garage.
Wide straps at the bulkheads.