You must use either a Q-tip or a stiff paint brush to apply spackle to all of your gable edges and then touch up their paint. The siding never is perfectly flush to the gable joints so spackle will fill in any tiny gaps. This is a must step before you install your gable gingerbread trim.
Do not try to use your finger to do this because it will just glob spackle on your siding and it will lose definition as it gets close to the gable. A brush will help you get the spackle in the gaps and not under the siding where it will glob in the overlap.
