I made the keyhole cockpit following Nick's notes. Since it is just part of the recess, which is fibreglassed,it should be strong. The boat isn't quite finished, so I haven't paddled it yet. I have sat in it and the placement is good(for me, anyway). For cockpit dimensions I used the West River offsets published in Sea Kayaker magazine a couple of years ago. The West River cockpit offsets are also in The New Kayak Shop book. I also think if you just follow Nick's picture to scale you will be fine.