Most of us who've worked with Fosshape to make costume mounts have experience the problem of removing it from the form after shrinking. The stress of pulling it off makes weak zones and creases, and you are left with an open seam to try to close neatly. I experimented with a different approach, making the foam original as a four-part mold that can be pulled out of the finished mount without having to split or fold or stretch. This approach makes a much cleaner mount that can be used as-is or covered with fabric.
I have found that by sewing darts into the form it gives it a little more strength and allows tighter shrinking. Having that nice clean seam along the back also helps support the garments, and looks good even if it shows. It's a little more work, but worth the effort. And, fear not, even with my neanderthal sewing skills I was still able to make something pretty decent. I've attached photos of the process. Feel free to post questions or comments here.