@John *****************
so you already did TWO visa-exempt entries since the recent 3 months, in June and July, and the next one will be on October 1st, and another one will follow right away when re-entering in November, coming from Vietnam.. . . . .While it speaks for you that you didn't extend, i.e. maximized each "touristic" stay, and do not plan to maximize the planned two visa-exempts in October and November, I would not risk to get denied entry at the border, because an Immigration officer comes to the conclusion that you are misusing touristic entries for a longstay. Make sure you got the THREE famous proofs on you in case you will be pulled aside both in October and when returning from Vietnam - 20,000 THB or equivalent in cash, a few nights booked accomodation and proof of onward travel out of Thailand within the 60 days