Leester and Marv,
To clarify, I use the Nitrate up to and including the attachment of any covering. I have found the nitrate attaches covering better than butyrate, in my experience.
I use Supercoat only on the open bays after the covering is attached. That is the only "shrinking" dope that I use, and only on the open bays after the covering is applied.
Since I use the Supercoat then I have to keep on using butyrate over those areas.
To go back to nitrate over the Supercoat will cause a mess. I have never had a problem using any other "type" butyrate over the nitratre.
As to fillers, I use several, mainly depending on what I have in the shop, and how much of a hurry I'm in! hahahaha
I use talc in dope, zinc sterate in dope, or automotive primer/fillers.
The auto stuff is the quickest. I use Dupont "Fill'n'Sand" through the paint gun, or Duplicolor Primer/Filler in the spray can. I have had no problem using any color coat system over either of these; dope, acrylic lacquer or basecoat/clearcoat.