Thank you for your time and energy devoted to answer my question.
I am not a US national. But I found your advice sounds very useful.
Please allow me to forward some more queries.
1-Don't I have to apply for TIN until I really need it?
The dramatical change of my personal circumstances is unlikely though.
2-No penalty for a tax resident not having TIN(not proposed)?
3-How long does it take, from the application to the actual issue of that number?
4-Is it easy to sort out tax return on your own(not relying on an accountant)?
5-When I lodge tax return in Thailand, do I have to declare my whole annual income back home(including the amount not remitted to Thailand)?
10% non-resident tax is taken from my interest income.
Do I need to submit any papers to prove it is already taxed home?
6-Once you get TIN, does TRD contact you periodically?
I thank you again for your kind reply.