Sew the squares into 3 piece units, press to one side.
Then, sew two units together BUT, in two different ways.
Set 1 sew with the seam allowance toward the needle.
Set 2 sew with seam allowance away from the needle.
Keep these sets separate, and sew a solid 6 1/2 by 2 1/2 inch piece on to each set.
Set 1 press all seams to the solid fabric.
Set 2 press all seams away from fabric.
Sew two of the same set together. Pictured has set 1 on top and set 2 on the bottom
Then, using one section from each set, put together into one large block.
All this sorting allows for the seams to nest. Eventually in putting the top together there will be some twisting ones, but I can live with that. If you wish, you can make all the rail fence blocks the same and just deal with more twisted seams.