I haven't added them yet. I'm now sewing the batting triangles to the back of my wide tri border after trimming the excess batting off the trapunto. I cut out some triangles of batting and I'm snuggling them up next to the pieced tris batting....and sewing them together just like we did for the batting squares in the center section. I decided that I didn't want to use a long strip and have a double layer on the pieced tris.
But it makes sense doesn't it?