I'm not sure I'd want to use a high loft batting on a Laura Heine projects. As you said the Steam A Seam makes it very stiff and I'm not sure you could get the trapunto type look that you seem to want. I'd definitely try it on a sample before trying to quilt the entire thing. As QuiltMaine says, Laura recommends quilting it pretty close together so that you catch the edges and she doesn't use a high loft batting on her quilts.