No worries if you are going on June 13.
Here is what you should do.
At Changlun, look for this agent:
The coordinates are:N6 25.502 E100 25.713
There are a number of such shops in Changlun but this is the one I usually go to. They offer good rates for Thai Bhats and you can also book your hotel through them - much better than walk-in rates. You can buy your Thai Third Party Motor Insurance from them (I think it is RM16 for 9 days) and let them print out your entry cards to save you filling them (and making mistakes). I think they charge RM2 per passport.
Then you can go to the Bukit Kayu Hitam Duty Free Shop. No limit to your purchases for entering Thailand (and nobody checks you in Thailand anyway). Parking is free if you purchase above RM100 but must remember to get your parking ticket stamped at the DFS.
After the Duty Free shop, you will reach the exit point for Malaysia where they want to tally your Car Registration card with your passport and your face.
Then you come to the Thai Check-Point. Look for the sign that shows CARS ONLY and enter that lane which is in your 1 o'clock position. Once in the lane, ask your passengers to alight and start queueing for the
closest booths
to the right of this car lane. There are many booths but for importing a car into Thailand, this is the
only booth you must use. Then you have to drive past the booths to turn left into an open-air car park and park your car there and come back to the booths on foot. You must have your passport stamped first. For that you have to insert RM2 (as the 'processing fee' though I can't remember exactly RM1 or 2) into each passport and smile for the camera. Ask the Insurance agent at Changlun for the correct amount and prepare the cash.
Then the car owner goes to the next booth to submit the car registration card and passport for an Import Form to be printed (free of charge - Betong charged RM20). Bring your documents and this form to the next booth and sign the form in front of the officer. Then you will be asked to collect your car.
You have to drive through the same car lane and as you pass the last booth, stop to pick up your Import Form. Then you are cleared to turn right to enter Thailand. Don't forget your passengers.
On your way out of Thailand, you have to do the same and make sure that you sign the Export Book when you hand in the Import Form to evidence the re-exportation of your car otherwise your car will be denied entry the next time you try to enter.
Not difficult but just time-consuming and confusing if nobody tells you what to do.
Enjoy your trip.
Please remember to record as many POIs and tracks and give them to me especially in Phuket as I map Phuket as well.