I use an i-taste MVP v2 with i-clear 30s.
If you change up juices I'd think keeping filled i-clears in your lunch cooler wouldn't be an issue to work out, they don't take up a bunch of space. As for waterproof, smokes have never been waterproof so ... keep your stuff dry the same way you kept your smokes dry.
As for safety of batteries, I'd say the MVP likely comes out on top in that it has all its safety features built in from charging to discharging and length of draw limitation (easily longer than you could ever need, but safe for the battery).
I'd go with the MVP or several if you like or ever feel the need. Its pretty rugged, and not so costly that if it turned up missing it would be a total loss.
I know back in the day I'd have had to smash someone if they stole my smokes, I'd do the same if they snatched my vape gear regardless of how much it cost. I don't think it happened that often, so...nobody likes a thief.
Maurice