Jonathan Pressburger They are probably not looking at the details at all. I wonder if two deposits would be ok if you could back them up with proof such as a pension statement and Social Security statement.
I believe the seasoning of the 800,000 baht is two months prior to your application for a 1 year extension and not the date of expiry of your permission to stay stamp. I would deposit the money 3 months early just to be on the safe side. You probably can apply at least 30 days before the permission to stay stamp expires.
I filed my 90-day at CW a couple of weeks ago. No TM30 required if I remain at the same address. You will need a TM30 to get a 1 year extension. I am doing something similar this month. I will go and return from the US and get a new TM30 upon my return. I have one unreported trip to Pattaya so I expect I may be fined for that when I go for my 1 year extension in October.