sorry I found this so late. I do a lot of wool felting and have made coats and vests and wallhangings. To join the pieces together I use a zigzag three or 5 stitch used for darning or in sewing elastic together and I use clear filament thread. After they are joined, I use a strip of double knit polyester (which will not ravel) laying it over the joined seam and then zigzaging with matching thread at about a 2.5 or 3 width and 2 length. If you are going around a curve, sew the inside piece first and the outside will stretch to fit. I have found some velour knits that will work also. You could use double knit wool jersey also.