The one I'm doing now I have the sashing separate, added between blocks in the rows/columns, then long strips between sections.
What I want to do next time is add the front sashing to top and one side of each block (two sides on final column and top and bottom on last one in each column) before sandwiching and quilting. Then do back sashing like method B in Kimberly's tutorial on this board. Think it would be quicker and look better.