If you spend more than 180 days outside Thailand in a fiscal year and then transfer money into a Thai bank account, will these funds be considered non-resident and therefore tax-free?

Being a non-tax resident depends on the amount of days you are in the country, but you have to be careful that you don’t accidentally become a tax resident in a jurisdiction which could have a tax implication. If you are planning to become a non-tax resident and transfer assets to Thailand, I recommend you seek advice regarding where  you will remain for the rest of the year before doing so.