If you did 2 pieces, the join would be right in the middle. I think the zipper idea is good, but I would do 2 zippers, making the quilt 3 sections. If it's a bed quilt, then put the zippers along the edge where the mattress ends.
But getting back to the quilt, 8'X8' (96" X96") is about a queen size. Mine are usually 90 X 100, I use warm and natural batting and my queen size quilts fit just fine in my average size washer.