If the temperature where you store your flavours goes beyond 30 degrees (86 deg F) you should look at various methods to keep them at a lower and more stable temperature. This also applies to fairly drastic temperature changes, as well as excess cold. Flavours, as with wines and olive oils, prefer a more stable environment; again, without direct light and heat.
Grab yourself a wine cooler and keep them at a near perfect temperature of 18 degrees (64 F). You can pick one up for $100, so they’re worth the expense when your inventory is over 100 or so. This way, they should last at least a few years. True, an extreme solution, but this is how I store all my flavours in summer. IMHO, most fridges are a tad too cold.
An Esky – cooler can work well too. An Esky, with or without ice, depending on temp extremes is suitable too. I used to use them when temps got above 30 deg. (86 F). I simply put some flat plastic ice mats in the bottom, placed an old rag or thin piece of wood on top, and placed 2 nail polish racks inside and keep the lid closed. Mine is the Willow 25 ltr version.
See our post on Steeping and Storing e-liquids.