you can not get registration without compulsory insurance. Not the voluntary, the compulsory. Same as in Australia. It can be paid at the time registration or you can get your own and bring the document.
Also must be shown with the driver's licence it was obtained with. Technically good for 90 days each trip in Thailand, but police never checked how long I had been in the country. Insurance might check. Also some insurance policies require a Thai licence. You can easily get a Thai licence if you want to stay longer.