I would suggest looking into how they make peking duck. Basically give your duck a bath in some what boiling water to help melt some of the fat away under the skin. then air dry it for it about a day then grill.
When I do duck, I brine, butterfly then smoke it at like 275 until an IT of 135, then I have a scortching hot cast iron skillet and brown/crisp up the skin, then I eat it and have a beer and pass out, but that last part is optional
I would spatchcock (remove the spine and flatten), and cook over indirect heat with a pan underneath to collect the goodies. A good brine and rub will add all the flavor and moisture you need.