It's all up to you, for koverall, I know it's properties, so attaching the tail feathers before covering, isn't a big deal, koverall shrinks alot, but for a first time job with it, I recommend covering them seperate and then attaching them after. If you've workked with koverall before, then go ahead and attach the tail feathers and cover it as an assembly. just becareful of warping the structure from the shrinking.