I put 3 additional grommets in the head and foot of the sail (for a total of 5.) This way, there is a grommet in the corners, one in the middle, and a grommet centered on each side of the middle.

The yard and boom are a little over long so I can pull the sail as tight as possible. I attach the yard and boom with zip ties. I use the same 5-attachment point setup for the battens.

I zip-tie the ends of the batten to the outside grommets, then take a hot nail and poke holes through the sail on either side of the batten in the middle and so on. Zip tie the batten to the sail through the hole.