I use the Hobie Mast Cradle (page 35 of their catalog) in the back and a bungie cord around the mast where it sits in the mast stand - I lined the mast stand 'Y' with foam (using zip locks) to cushion the ride. This works well.

To secure the boat I use a line around the front cross bar (where the mast attaches) to the trailer and use two webbing/buckle cams from Lowes accross the boat. These webbing/buckle cams allow me to carry the sail on top the the tramp (tieing the sail back to the post where the mast connects to the front cross bar).