Consider easing back on the vaping in the days/hours leading up to the gig. It's still hot vapor that isn't great for the body. Higher nic might help prevent desire to chain vape. Then you can chain vape when you get off stage
Few more tips you probably already know: room-temp (or better hot/warm) water with honey/lemon (no cold water!). Warm up your voice properly. Don't drink coffee or caffeine in hours before a gig. Caffeine and cold liquid constrict vocal chords. No milk or thick liquids.
This is some SOUND advice lol. I entertain most every night of the week and drink only room temp water on stage. If I am having any issue I use a pastille called Euphon which contains Glycerol (VG) as already mentioned. I vape very occasionally during performances and my liquids are minimum 50/50; high PG dries the throat too much. In theory, vaping high VG juices on stage should help plus adds a nice mist effect to the stage lights for which you can charge extra