I'm sure Blueskytoday will agree that unless you know your way around Seoul and speak some Korean the chances of finding gay places and getting to know any Koreans will take so much time that you'll be on the plane home before you realise it. Very much like Tokyo, but at least in Tokyo it's not that hard to find the few bars and saunas etc. that welcome foreigners. Bear in mind, too, that since it is rent you are after, few will know much English, if any. Other cities in Korea? Same situation but even more difficult.

For a relatively problem-free short trip not too far away from Shanghai where MBs are available and there is virtually no language problem, Manila really is about the only solution. And it's a helluva lot cheaper!