My experience was to keep withdrawal receipts from foreign bank .Declared with country origin airport before leaving,given receipts. Declared with Thai immigration when entered,given receipts.Deposited in Foreign Currency account with my local bank for one year. Baht was strong at the time so never converted. Used bank statements to satisfy immigration. Now with baht strong have gone to monthly 65000 deposits and withdrew the foreign currency. Declared the foreign currency when leaving Thailand and returning to country of origin. Depending on currency,the 800k has become a lot cheaper to maintain. But I never exchanged to Baht. Hope this helps.