PPC Hi there!
After you install Sandboxed Google Play (GSF, Play Services, Play Store) and go to Settings > Apps, you should see an entry named "Sandboxed Google Play" right under "Default apps".
If you do not see that, could you please send us a screenshot of what you see on that screen, as well as another screenshot showing that you have all of those 3 apps installed on that profile?
Looking forward to your reply.