I have joined pieces several ways......if you do it before you sandwich...you can lay one on the other overlapping a bit and cut with rotary in a wavy line rather straight across, then hand whip together. If you sew by machine, be careful that the seam doesn't leave a "ridge". If it is poly it can be "pulled" on edges and then they can be blended together. Sort of like carding wool....I am eager to try the new bonding tape...hmmm never thought about using fusible interfacing...good idea.....