Hi Nigel, I am no expert but I will say that Thai immigration are quite strict about the ฿400k and the two months period. I accidently went below the limit by ฿750 and they rejected my application for a Non-O spouse visa.

I said to the Immigration officer that the money had already been in there for three months prior, he agreed, but at the time of the actual visa stamp, you need the ฿400k to be there for two full calendar months.

I had to get some other visa extension to a wait for the funds to mature, I go back in January to await the result. Good Luck!