you need 3 months worth of statements but the most recent statement needs to show 800k baht in the account. Just went through this in Laos last month from Nong Khai immigration.
The problem I see is if you transfer from Bangkok bank to Krungthai it doesn't show as an international transfer at this point and it might negate the whole process. If you open a Krungthai account you need 400k transferred in there from your home country from everything I have read and seen. I could be mistaken as I do know for a non-o it has to show as an international transfer to be accepted.
when I left Seattle last month without a visa, I was asked about onward travel. I explained to the lady that I would get a visa from Laos before the time was up, showed my 800k in Thai bank and a bus schedule to Laos in case that didn't work. She was fine with it. BKK IO asked the same questions and I went to the same script as before and he said ok, have a good day". I previously came in on 90-day non-o's in November and April to get my bank account all squared away. I think being prepared with answers may have helped me or I was just lucky. I'll take it either way 🙂
I just got my 90 day non-o last week in Vientiane. Got there Monday afternoon applied and then paid Tuesday morning. Had to get a couple of my documents corrected (completely my fault) and had an approval Thursday morning. Would have been ready Tuesday most likely if my paperwork was in order. Came back to Nong Khai Thursday afternoon.