Tim,

I have used Rustoleum primer and Minnwax with talc for a filler.  The talc takes fewer coats than the primer, but I have always brushed it on and the brush marks are a pain to sand out.  I prefer the primer, just takes lots of coats.  The only way I can tell if I've sanded through the Minnwax is when the wood starts to fuzz.  I can also feel the difference in the friction of the sand paper as I start to sand into the wood.  Having said that, I don't sand to a perfect finish until I start using the primer so I seldom ever get to the wood.  The primer will fill any slight roughness of the Minnwax.  I've tried wet sanding the primer, but it's more trouble than it's worth.  I just keep wiping the paper on a dry towel to keep the grit clean.  Hope this helps.

Paul

I would say if lyou appllied silkspan over the base coat you do not need talc or sterate in the clear/primer coat.  Put two coats of clear over the silkspan and rub down the roughness.  Very fine sandpaper.  Two more coats of clear and sand.  You should be getting a kind of matte/shiny finish.  It really depends on how thin you do the dope.  The way I thin dope it usually takes 4 or more sessions of 2 coats and sand.  Let the dope set at least a day before sanding.