If you wanted to copy a zero nicotine version of the pre-mixed nicotine vaping liquids then you would need Propelyene Glycol & Aqueous Glycerine, mixed at 80% PG to 20% AG.
But you could mix them in whatever proportion you like, the great the percentage of PG, the more throat hit you will get, the greater the percentage of AG the greater the vapour output is, the DV flavour concentrates use a PG base so this needs to be figured into your overall PG percentage e.g:
15% Flavour in PG (total percentage of PG is 65 + 15 = 80%)
PEG 400is supposed to be an "all in mix" that is it gives you good throat hit and vapour without having to mix (people who feel they have a reaction to PG can usually use PEG 400 as a substitute) the downside is PEG only performs well in a fairly new atomiser.
I hope this helps