I think that trying to attract dragon / damselflies to a bog garden is a bit of a non-starter. The larval stages need plenty of water space, and a reasonable depth.
One thing that you should be wary of is putting too many holes through the sunken liner - take it one fork at a time until you find the optimum drainage. I made the mistake of making too many perforations, and the water drains so quickly, it hardly qualifies as a bog garden.
JeremyB