@Paul ******
I spoke to our shippers on this last week - they said without a min 1 year Thai work permit you can still import household items but everything is potentially liable for 20% duty on the new replacement cost (whatever the Thai customs deem it to be, regardless of your receipts)- even old and used items are subject to duty.
But from reading other forums it depends on which person processes your paperwork as to how much duty is deemed due.