I hadn't heard of doing trapunto by cutting and stuffing - learn something new every day!
I learned a different way - layer the top with a higher loft batting (like poly) and stitch around the motifs with water soluble thread. Turn over and trim the batting right up to the stitching line; sandwich with regular batting and backing, then quilt, stitching around each motif again and doing a dense fill in the background.
I'll have to check out this other way - thanks!