you drive to the wharf in Ranong and catch a boat out to an island it's part of Myanmar go through the immigration checkpoint can walk back to the wharf wait for the next boat back to Thailand go through Thai immigration or you can stay the night at the casino on the island and get duty free
Insurance still won't cover you you can get accident insurance from most banks for about 5k baht good for public hospitals only covers you for 150k plus your rego insurance is 30kbaht only covered if you have international driving permit or Thai licence to ride