if you are using dope, or lacquer primer, you can use non-catalyzed lacquer glazing putty,, one tube lasts for ,, oh about 15 or 20 cars,, so thinking it might be forever on airplanes,, I would suggest the FIRST most important task is to minimize the dinks, gouges and screw-ups that you need to fill,, filler is always,, ALWAYS heavier than balsa, and generally harder,, so less desirable,,
in other words, ,naked balsa never touches anything hard sharp or pointed unless you intend it to,, so remove all those spare electronic whatzits from your bench,, the random car or truck parts,, and anyother thing that is not part of the plane you NEED to have on the bench,, then stay away from the lights when you swing the thing around,,
aside from that, superfill is the be all end all,,or if needed the dolphin glaze, ( i prefer evercoat myself)