Can I use my funds from a marriage visa in Thailand, and is there a seasoning time before reapplying next year?

Basically, you can use your funds once your yearly extension is granted. But better to ask your local immigration office. We are aware that one or two offices would check if your funds are still in a bank account when you are back at the immigration office after an unde-consideration period finishes.

You need to have your funds of 400,000 baht sitting in your bank account for the full two months as of the day of your APPLICATION for the next yearly extension. Not two months in advance to the end of the current extension.

You also need to check this with your local office for their policy.