I just shipped a new CURVE kit to the person who inspired the first CURVE. He needed a neck rest that would not just provide front-to-back cushioning, but would also secure his neck side-to-side. I searched for something I could use for a light but solid base, and eventually I discovered 8" high pressure water couplings. I cut one in half into two cylinders, and then cut one of the cylinders in half again. That became the first (and only) half-wrap CURVE. After working on that one neck rest for a while I began to think it might be really comfortable for other folks as well...if it didn't wrap quite so far. And so the CURVE was born.
The Axiom Trekk seat collar is a terrific find because it comes in a size (31.8) that will fit the vertical tube of a "T" tower. It's a potentially great way to secure your rear rack right to the neck rest mount. You may be able to find it at your LBS, and I know it's available on Amazon.