i have done the same technique but using a wide round brush used for craft painting, I think its called Tole painting, and Mr. Surfacer 500 for the cast technique. it will fil in with paint later but hold washes well.
Back in the day, and we are talking 1985 here, spring to be exact, I set forth to the hobby shop on my meager E-1 Private pay and layed down an entire $7 for this kit. I was thrilled with it but just could NOT justifiy paying upwards of thirty dollars for a model kit, hence my lack of a Nutrocker or Fliedermaus.
I still have this model and display it during our annual library displays.
Build to please yourself, and don't worry about what others think!
TI 4019 Jolly Roger Squadron, 501st Legion