Mine are in a carboard box or tool box. Hot, cold, in between, no effect. I believe there is in general nothing to "go bad" in them. The only one I have to be careful with is my own tobacco essence that I make from pipe tobacco and VG. That one will turn nasty after some weeks, but then it probably has plant biomolecules in it that bacteria like to eat. Bacteria don't like PG (most common flavor vehicle) or simple flavor compounds. No food there, and PG just kills them, as does alcohol, which is in some flavorings.
I cannot comment on the natural organic flavorings that are becoming available. If they are extracted from plant/fruit/coffee directly and then purified, there may be an issue. Vaping is the one form of ingestion that I prefer everything to be simple chemicals, not only for shelf life, but atty preservation, and less health risk with inhalation. That said, I would so love to recreate Vaperite's Kona Cream, which they claim is all organic and VG only. OMG it is delicious!