John, I don't know anything about Oratex, but on my Polyfiber wings I did use reinforcing tape and rib stiched the middle underside tank rib. I felt much better having this slightly concave area rib stitched. I spaced that rib from the tank using small wood blocks located between stitches, leaving a small gap between rib and tank for the stitching. I used a small, very flexible wire for a needle and used a separate piece of thread for each stitch. Took a little bit of finese but was not difficult.

Per the book, I ran a 2" finish tape on the top centerline of the rear spar, before putting on the rib tapes. The fabric is so close to the spar on the top that any motion of the fabric during flight would cause it to contact the spar, which is why you need a reinforcing tape in that area.