PG and VG may slowly degrade, but both are easily available and cheap. Personally, I only keep liter amounts of both around as I can get more with free shipping on Amazon. Nic should go in the freezer, preferably in glass bottles. Keep a small amount out for your usual mixing needs. When the little mixing bottle is empty, pull on of your larger glass bottles out, refill, and return the larger bottle to the freezer. Nic should last many years if kept cold.
As for bottle size, I'll buy a liter at a time and split it up into 250 ml glass bottles for long term storage in the freezer.
I have 1 large glass bottle then a bunch of smaller glass bottles that I put my nic in. That way when you pull them out of the freezer (wait till they are completely defrosted because if you open them before the are room temp it will suck the moisture out of the air and cause it to degrade faster (FYI I live in Florida where we have high humidity). When I'm finished or close to finished with a bottle of nic I will pull a small 30ml out of the freezer and wait till it's room temp then use while sitting my used bottle to the side so when all of my small bottles are empty I will then pull the larger bottle out, defrost then fill all the small bottles and return them all to the freezer.
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