of course not. He could go to any border, park the car on the Thai side (they all have security parking in these places). Go with the flow, cross the border, check out of Thailand check into Laos, stay buy some banana in Laos, eat the banana, turn around in your heels and walk right back to Thailand. Well it will cost him the Laos Visa, but hey he is going to spend valuable capital
my pickup is in my own name and I crossed the border to Laos in my own Thai registered car many times already. You need the magenta book, a "TH" sticker on the back of the car and buy the insurance right t the border
for Myanmar I do not know. For Laos the car needs a Magenta Passbook issued from the Department of Transportation from where the car is registered. This book enables you to cross the border to Laos. In Laos he has to buy an Insurance. Everything is fluid, a lot of people do that
no, Thai cars are not allowed in Vietnam due to right hand steering & no valid drivers license. Can enter Laos and Cambodia but not yet Vietnam. Maybe sometime in the future
you can also apply for the Extension of stay based on being married to a Thai inside Thailand. This will give you a full year and save you from doing the 90 day border runs. However for this you need to meet the financial requirements