A way to split the difference:
Establish a ThB400K term account to qualify for your marriage with Thai wife extension.
(also known as buying a Nissan March and parking it in the carport, unused)
Remember to let the US Treasury know you have a foreign account >USD10K by filing a FBAR report (FinCen Foorm 114).
Once you have a regular passbook account established, have your bank complete their section of the ssa-1199-op107 form (Direct Deposit of Social Security into a Thai bank account).
Submit completed to Federal Benefits Unit in Manila (FBU.Manila@ssa.gov) who administers all federal benefits for Thailand.
Every month your net Social Security payment (after Medicare and withholding) is deposited into your regular passbook account.
Next year present your bank letter showing your:
1. Direct deposit of your Social Security payment into your passbook for the preceding year
2. Sufficient funds in your term account to total ThB800K.
Request extension based on retirement rather than marriage to a Thai wife using the combination method (note combination is not available for spouse extensions).
This avoids depositing ThB800K into a Thai bank (AKA purchasing a Toyota HiLux double cab pickup and parking it unused in your carport).
Splitting your qualifying between income and deposit gives most of us outside of urban areas enough monthly Thai Baht spending money once the house is built and the vehicles bought.