If you are already in Thailand, you may have to work with the Manilla FBU and that will take months.
While you are doing this, you may have to change your SSA address to Thailand. That may bring about Proof of Life notices every year or so depending on the type of address you do (mailing or physical address)
What is a proper visa? I enter and leave several times a year for a stay of about one week. I am not going to pay for a DTV. I live near the Cambodia border. An expensive visa is overkill.
Is it a drop-down list or fill in the blank? Most Thai forms seem to use a list which helps a lot. In any event, it will be difficult for the average tourist.