'Plugins' folder - Drag and drop this folder into your metapackage's 'Content' folder. You will need to modify the InstallerSections.plist if you have any additional Installer plugin bundles - otherwise, it should work fine per-default.

'Info.plist' - This is an example of the metapackage's Info.plist file. Do not overwrite your metapackage's Info.plist file with this one, but rather add an IFPkgFlagUninstallList Array along with a String property specifying the "PKG_REF" of your package.

Information regarding "PKG_REF":

The PKG_REF of a package is relative to its position in the installer - that is to say, if you have 3 packages within your Installer, their PKG_REF will reflect their ordered position in that list:

Package_1.pkg -- PKG_REF_1
Package_2.pkg -- PKG_REF_2
Package_3.pkg -- PKG_REF_3

To note, PKG_REFs actually start at 0, however PKG_REF_0 refers to the metapackage itself, and as such, should generally not be specified.