That is going to be a stunning quilt. What kind of quilting design are you trying to mark? If is is just straight lines I would use masking or painters tape. You could even cut designs out of contact paper stick it where you need it. Quilt around it and move it to the next location. I have done both many times. Marking is always a problem. That is why I prefer wholecloth quilts or cheater's that I just quilt around the motifs.