It's fairly straight forward if you have the funds deposited in the bank. We've been here three years - always keep our balance above 400K baht each (Joint account so 800,000 baht) making sure we have
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0 baht each (1,600,000 baht) 3 months prior to renewal and 2 months after. Supply bank book, bank statement, bank certification of account letter, lease / TM30 with the ID of the land owner, passport photos and passport and proof of 90 day check in being compliant (at least thats what Hua Hin immigration required 2 weeks ago) and pay 1900 baht. (2000 baht if it is first time I think? ) Took us about an hour from walking in to walking out with our stamp.