Store your Nic base in a big glass bottle and in the freezer, it thrives in the cold. I Transfer mine right to a glass bottle, and I also fill 3 x 30ml bottles and always take from and use the 30ml bottles first, once all 3 30ml bottles are empty I then fill them again from the big bottle. This way my main big bottle gets opened much less so less oxygen gets to it. So far in almost 3yrs this system has proven to work best for me.
PG & VG by them selves last about 2 yrs, VG can last a bit less then 2 more like 1.5 from my results.
However once you make a juice the flavorings are what end up going bad the fastest, the fridge has proven to store my DIY and purchased juice the best. I store my juice in the fridge till I'm ready to use a bottle then take it out and it stays out, but new bottles of juice not in use I keep in the fridge always. Just how I do it anyways