TLDR : Answer Summary
To apply for a DTV 180-day extension in Thailand, you essentially need to re-submit all the original documents required for your initial visa application, but updated and freshly dated. Commonly required documents include: passport bio page, copy of the DTV visa, the latest visa stamp, a recent TM30 printout, TM7 Visa Extension Form, updated bank statements (a minimum deposit of 500,000 THB needed at least one month prior), proof of residence (house rental contract), receipts for rent transfers, and any relevant documentation to support your stay, such as course enrollment for classes. However, requirements may vary by the immigration office, and in some instances, it may be less hassle to leave Thailand briefly to reset your visa.
DTV VISA RESOURCES / SERVICES