Here's one I haven't finished yet (started in FM Pro 12), but the basic setup is there. When I upgrade to 14, I will re-do it with all the newer features:
Pick it apart and see how it's set up (relationships), and the navigation scripts. The letter/message writing is the part that's unfinished. I want to delete it and go a completely different way.
Don't forget to unzip, or you wont be able to enter layout mode
Enable "allow creation" for the link from the layout's table occurrence to the portal's. That allows you to create new join table records to add participants. You can include fields from the participant's table in the rows of this portal to the join table. You can format the participant ID fields with a value list of participant IDs from the Participants table.