Would this just be a one-layer quilt?
Usually when you sew fleece together you overlap the seam allowances and then use a zigzag or decorative stitch to go down the middle.
It might work to "rag" piece them. That is, make normal seams but allow them to face outside. The seams won't fray, of course.
I think fleece is usually used in one piece as a backing for a quilt because piecing fleece makes the seams so bulky (unless you overlap the edges as described above).