I also read from a 'Visa guru' (Maybe the same 🤷♂️) that IF y'r Embassy still issues an income statement, that it's even not possible to use 12 month deposits for the year extension. Besides the 800k฿ path ofcourse.
Well, look to the (very long 👍) answers of Andreas.
Especially the answer on an income statement from y'r Embassy in Bangkok. That prevents you from putting 800k฿ in a Thai bank.
However I would open a bank account for sure (with the non imm. O visa) and start transfering 65k฿-plus, in that account every month. You can use it immediately after it is in. I mean you need money to live in Thailand anyway ofcourse. This I mention also as a tip because more and more Embassies stop giving such an income statement.
E.g. Canada and I thought Norway already did this year.
Then you have no real problem to get a new year extension should the Belgian Embassy also stop.
Continue this also when you are those 3 months in Belgium.
The route I followed: (8 years already)
Bought a non imm. O single entry
Arranged an income statement from the Dutch Embassy in Bangkok (For Netherlands it's called 'visumondersteuningsbrief' 🙄)
Gathered all needed forms for a year extension, like TM7, STM2, etc.
Went to imm. office after 60 days in Thailand and got the year extension for 1,900฿.
(If you want to leave and come back on this extension, you also need a single re'entry permit to keep y'r extension alive. Form TM8 and costs 1,000฿)
Then every year you have to come back to Thailand before y'r expiration date of that year extension and repeat everything concerning the year extension and re'entry permit.
Wow. That's a nice deviating rule over there without income statement 👍 So also the Swedish Embassy in Bangkok don't give an income statement anymore ? (have 2 Swedish friends, that's why I ask)
With me the Bangkok bank app. did not work. After I removed vpn and virusscan app (Avast) it worked. After re-installing the vpn and virusscan, it kept working. Maybe worth a check if relevant 🤷♂️
Y'r last name is Dutch/Fries. If you have a Dutch passport, you still can get an income statement (Visumondersteuningsbrief in Dutch) from the Dutch Embassy in BKK.
And I think you mean getting a year extension (instead of mentioning a non imm. O-A). With y'r imm non O, you should be able to open a bank account (if you not already have it) and indeed put the money ((800k฿) 2 months before applying for that year extension).