@Mark *******
You can literally fly out and straight back in. It's the entry that reactivates it, as it's a multi entry visa. You can go out and in as often as you want within the 1 year validity. It's the insurance that determines the length of stay.
Example, you enter Thailand first time with insurance and are stamped in until the end of your insurance (approximately 1 year). Then you leave after 3 months to go Vietnam for a few hours or a few weeks. Then you go back to Thailand and you get a new stamp which should match the exact same leave date as your last stamp.
The trick is, leave Thailand just a few days before the visa issued in your country expires. Then come back with a new 12 months policy.