If you live in an area that experiences temperature extremes, you might want to reconsider leaving a SSC in your car. The extreme heat and extreme cold can really wear on the plastic buckles, and you could weaken them, lessening their life. Worse case scenario, it could break while you're wearing it.
I live in an area that experiences all four seasons, so I tend to leave my SSCs in my car in spring and autumn, bringing them inside during summer and winter. This isn't too much of a hassle for me since I already bring in my diaper bag during winter/summer to avoid ruining my diapers, freezing my wipe solution spray bottle, or melting my little one's diaper cream/stick.
If you have a a mei tai, woven wrap, or a ring sling with metal rings, I'd recommend leaving these in your car over a ssc. Not only will the temperatures not matter, but in cold weather the wrap or ring sling can serve as blankets for your little ones (just unthread the ringsling).
|Vanamo wrap - Kide Tuli - as a blanket|
Disclaimer: Thoughts of Fluff was not compensated for this post. All opinions are my own and may differ from those of your own.