Someone I might know had an expereince goign through and being in a country that has a strict no Vaping policy.
They took a simple cheaper mod that they it wasnt the end of the world if they lost. It also didnt outwardly look like a Mod. it was more of a box with internal batteries.
They took an RDA, but had it in a seperate part of the carry on bag.
They took 30 mls of juice, in their pocket, since there is no reason for anyone to check the pockets for an item that isnt metal. .
going through was completely fine. When the person went through security to return, One of the agents took out the RDA, Snickered and put it back in, since i was leaving.
Usually pretty lax with what you take out. It is what you bring in that counts, but since vaping isnt banned where you are leaving from, It will be fine.
Seoul has no issue. Not sure on China