There's no danger of my leaving any typewriters in direct sunlight or a windy place, since I do all my typing in the comfort of my home. I am concerned, though, about the quality of modern ribbons compared to classic high-end typewriter ribbons. It seems that people are so glad to be able to buy new typewriter ribbons at all that any discussion of fabric quality is unthought of. Many new ribbons I've seen have a visible weave and leave characters on the page that are made up of dots. Some classic ribbons were made with a very high thread count and left crisper, sharper character impressions. I'm not sure if those kinds of ribbons can still be found today.
Well, there is a difference between old and new material. But I think ink is the key. Typewriters had special formula, close to the stamp ink, but not so messy (i did revive one ribbon with it, and it made a bit "splashy" letters). My ribbons from the shop are ok, maybe not perfect (spools look weak, ribbons are nylon), but for now I'm happy with them ;) My SM3 is always on the desk (wife hates it's case :D), and in few months I didn't notice drying.