Correct, keeping mono tracks centered will split them to the master stereo track evenly.
Doubling mono tracks doesn't make sense from a workflow stand point because it's more steps for the same result and because you're mixing two waves into one so you're adding amplitude to the signal... not a terrible thing, you just have to compensate for it, but still another step.
Angelo Lorenzo
Fallen Empire - Digital Production Services
RED transcoding, on-set DIT, and RED Epic rental services.