I would quilt the flannel blocks and tie the chenille. I use a large needle and yarn. The ties should be no more than 5 or 6" apart at the most. I've used quilting and tying together on quilts with excellent results. Flannel is usually less dense and will pull apart after several washings when it's tied. I'd quilt it about 1/4" in from the seam line. It depends on the pattern you've used but I tie in the center of the blocks--less bulk to go throw. Also you might want to get some rubber fingers or rubber gloves to help pull the needle through.