I use BKK bank with the 800,000 in a fixed deposit account. Only access to the account is via personal visit with passport etc, no internet or ATM access.
The only transactions are the interest in, the withholding tax paid to the Gov and my withdrawal of the interest all on the same/next day.
Even so CM I/O now (last 2 years) require updated bank book, statements to cover the complete year and the bank letter.
A full one year bank statement takes 5 working days with BKK and therefore you need to get it ordered at least a week in advance and on application day/s collect the one year statement and then ask for a "last one month transactions" statement to cover the one week gap along with the letter.
The other option is to ask for a six month statements every 6 months which are printed same day as requested and then get book update and letter (and one month statement if dates do not overlap properly) on the same day.