VP files have nothing to do with campaigns actually. They are just a container file to help keep things neat and tidy, plus improve load times slightly.
What you need to do is first make the missions, then string them together using the campaign editor in FRED. This editor creates an .fc2 file, which is what tells freespace that your missions are in a campaign and how they are interlinked. Once all that is done, you can then pack the missions and the .fc2 file into a VP if you like, but this part is optional - Though certainly recommended if you plan to distribute it.