I opened an account in thr Chuang Rai branch of Bangkok Bank with just Mt passport, it took around 30 minutes, I was staying there for a month, we are going back for good later this year but good luck.
I opened a Bangkok account in Chiang Rai last November which took about 30 minutes, I can't remember if I had to show proof of an address in Thailand or not apart from my passport.
I did have an issue when I returned and the London branch couldn't help as there systems are not connected with Thailand believe it or not!