I saw a really easy way to layer and pin baste any size quilt on a 3 x 5 foot table in the book "Heirloom Machine Quilting" by Harriet Hargrave. She first marks the center of each side of the table by taping a toothpick to the center top edge of each side. Then she folds each layer one at a time in halves to find those centers and lines them up with the toothpick. You can feel it under all the layers. Next she clamps the layers along the edges with binder clips or clamps. Large quilts will hang over the edges but that's okay. The center of the quilt is pin basted first then the whole quilt is unclamped and moved to one side or the other, reclamped on one edge, and pinned. Then move the other side over, clamp and pin.
This is by far the least back breaking method I've ever seen to baste large quilts.