When I go each year to do my Retirement Extension, I must show 800k in a Thai Bank in my name only, having been there for two months (sometimes 3) before the application, OR transfers of 65k each month x 12, OR a combination of Bank deposit and transfers which add up to more than 800k. (Not all IOs accept this)
Also letters and statements for all pertinent accounts from each bank, copies of my Bank books which were updated ON THE APPLICATION DATE, copies of Passport pages showing Data, previous entries/visas etc. On yes, and the correct Form filled in plus Bht 1900.