@Christopher **********
immigration does not like the DTV visa and they do not want to process extensions for it. If you go to immigration to ask, they will suggest you do a border bounce instead. If you still persist they will give you list of requirements. When you return, there will magically be new items that were left off the list that you have to leave as obtain. Repeat this process until you they get you to give up or you run out of time.
One example: in Chiang Mai they require proof of 500,000 in a Thai bank account, knowing full well that you can't get a bank account on a DTV.
Another example: they require you to have 15 days left on your stamp or they will not accept your application.