Just make sure to not introduce high-heat as that changes the flavor profile. As said keep in dark closet or alike and top-off in-use bottle simply. It will last a couple years fine atleast, if watching the heat. If you have high-heat e.g. no AC in summer, then refridgerator or freezer is an option. The only thing that can happen else, is the VG can get thinner and thinner, as it's highly hygroscopic, but if not closing and opening a million times and it's not an amount to last many years then fine. If having longer lasting amounts than that, then it could be rebootled into e.g. quarts or something, but normally not really needed... If storing in e.g. fridge, then let come to room temp before opening, or else added moisture is drawn in upon each open/close cycle and will thin the liquid...
In my experience, then keeping under 30C is vital and the only real important thing actually to look for... Over 30C for pro-longed time either makes the VG sour or otherwise bad tasting... I mailed with a VG manufacturer, and he also stated that VG was pretty "rough" and stable under normal conditions, except high-heat e.g. 30C for more than a couple days at a time, which is the main thing to avoid, and i've dumped alot of VG down the drain because of that, as having no AC in summer-time where I live...