How to cook perfect meringue in a gas oven?
I usually go with residual heat.
But I use Pavlova meringue recipe (with teaspoon of potato flour) which call for baking for 30 minutes in 120 degrees (I adjusted time to around 18 minutes to compensate for the 130 temp).
Then I open it a little for around 2 minutes to lower the temp and keep closed for another 2 hours. 
When I was making typical meringue I just put a tray in the oven when the temp dropped to around 100 degrees on gauge (old type gas oven with gauge in the middle of the glass) and just let it sit there for 5-6 hours.