Incase anyone is planning to apply for Non-O Thai spouse in HCMC Vietnam, I would like to share my experience that may help others.
'2.5. Applicant’s financial statement of adequate finance is required.' Upon further enquiry via email 'Regarding the financial statement, kindly print out the transactions within the last 6 months from your bank account. Additionally, it is highly recommended that you have as much money as possible for the latest account balance'
There is no seasoning requiremnet for the funds but i assume they want you to have over 400k on your bank statement when applying. I provided 6m statement with over 400k as the final amount and received the visa per usual processing times.