I am building the Arado 76 from MAN plans. It is a light .26 size plane, about 3 lbs when done (hopefully).
While most of the plane is covered with Ultracote, the top is not,it is bare balsa. The plan instructions say to "fill the balsa so that it is smooth like metal, then paint.

I tried Sig dope sanding filler and it doesn't really do the job.
Can anyone suggest a filler that a)fills the grain; and b)is sandable. Thanks