I have made t-shirt quilts with rubberized shirts and lots of other types of materials. I prep the shirts by ironing the backs with a stabilizer and than stitch the cut pieces together. I than use fleece on the back and stitch in the ditch thus avoiding stitching over the rubberized parts or the t-shirt. Since we live in the south, a heavy quilt is not needed and the fleece works really well. I am in the process of make one for our granddaughter and one for our grandson using this method. It also makes it easier to wash and keep clean. So maybe I am not a "real" quilter, but it really works well for me. Like you I have expensive machines and do not want to mess them up.