Some suggestions that work for me. DO NOT ASSEMBLE IF YOU ARE TAKING TO A LONG ARM QUILTER as they do not like the spray basting. They will take it apart.
1. Tape the corners of the backing down to the floor tightly. This will keep the back from moving. You might even use a blanket underneath so no 'overspray' gets on surrounding area. No fun scraping up sticky residue from floor.
2. Spray lightly avoiding the edges.
3. Place batting on backing and smooth out.
4. Spray top of batting.
5. Lay or unfold the quilt top. And smooth out wrinkles.
6. Pin edges and remove tape from floor. You can roll up or fold if small.