If you are making blocks with designs that are mainly running stitch, and using wadding and backing in a 'sandwich', you do not need any interfacing or stabilizers to back your embroidery. I have done dense embroidery- minus the backing - and the wadding is a stabilizer. You can also hoop just the backing, and place the wadding and main fabric on top. You can use a little spray adhesive to hold them in place, or a couple of pins if you don't put them in the way of the needle, or sew a 'frame' around the edge, to stop movement.