It's a waste of time in recent years things have changed.
Ignore the bring a Thai friend with account at that bank or a Thai government employee etc etc.
I am stating from my own experience.
I have extensions from non O based on retirement and even big branches in Sukhumvit wanted a "certificate of residence " OR letter from embassy.
UK,USA,AU do not provide that for address.
Also 800k in your pocket will not help.
Fortunately I had success with Kasikorn, however I had a non O (not a tourist visa)
Also already had an account with another bank.
An agent can open an account with BBL.
Cost approx 4500b