I have followed the instructions in the SDK and am able to export a valid package. However the SDK Documentation states that..
Once you have added the Marketplace data to the package you'll want to preview it in the simulation. The first time you want to do this, you'll need to use The Project Editor option for Building A Package. Once this initial build is done you can preview how it'll look on the Marketplace by going to the Marketplace section of the Microsoft Flight Simulator UI, and it should be shown just like any other item:
I have done this, ensured that the Markplace data is contained within the built package, but the Marketplace UI does not show my airport? Has anyone else had this problem or know what could be wrong?