@Ben *****
HCMC and Hanoi are mandatory appt booked online consulates, if there are no openings it means they're booked
AND
they're both switching to online eVisa applications some time in Oct too, so that means you would go to vietnam, apply online, wait for the application to be processed (they are saying it's going to be extended time maybe up to 2-4 weeks) get the approval email then come back to thailand