I didn't need to. However, I did have to do some "questionable" paperwork. Every state is different in what they consider "residence", in most cases its a mailing address. I also registered to vote, got a driver's license, opened a bank account. The bank account was the most difficult because they wanted a real address (not my mailing service).
I use google voice. GV Requires you verify the number a couple times a year. A couple of times a year I have a friend in the US enter a text code that is sent to my phone. Hence, your GV will need to be associated with a active working number with a person to do the verification.
If you are officially volunteering you need to have visa/permit. That's not quite the same if you do it 'unofficially'.
If you have your own money and paying your way like a good little expat nobody is going to look at you a second time if you are serving some public benefit. Where you get into problems is when you turn it into a real job.
I am having a difficult time opening an investment bank account in the US from Thailand. If you do not have one already I would suggest you do that before you leave.
I use Google Voice to make/receive US calls. I would recommend you set-up something like that before you leave.
If you pay taxes in your current state I would recommend changing to a tax free state.
If you can renew your license before you leave that may be helpful, if you want to drive in any other countries. The International Driver's License is a myth and the International Driver's permit is not as helpful as some think it.
Thailand has no flat sheets so if you feel those are must, bring them with you.
I use a mail forwarding service which works pretty good most of the time (see investment bank account). I would recommend you set-up that before you come but it's not fully necessary.
I would be careful doing that. It may work out fine. Another thing that could happen is that you go through all the pain of getting that piece of paper, then your return to the original branch and they will request some other paperwork.
It could that what they are not saying is, they'll not open the bank account without some incentive (purchase of insurance, use of the cousin/agent, etc).
I would shop around at other branches, or the main branch to make sure they are all asking for the same thing. I think you will find they all want different things.