I'm an admitted grip-slider—I like to move my hand all over the grip and seat, depending on how I'm casting, and I do it without even being aware that I'm doing it. The problem is that most reel seats are uncomfortable, what with locking rings and/or skinny proportions. I gave up on factory grips years ago, their uplocking seats and flared butts not at all conducive to my habits. Ed Herbst in South Africa has come up with some designs that make it easier to grip his rods way down on the seat, but they are complex affairs requiring careful inletting and fitting. In the interest of simplicity, I've stuck pretty much completely with sliding rings on cork seats, going so far in the past as to make my own hidden keepers from titanium tubing. Sliding rings have their own problems, though. They slip, usually at the worst possible time. They are usually too small or, if big enough, uncomfortable under the hand. They dig into cork (largely alleviated by using only the very best cork for seats, and tapered rings). To keep the diameter of the grip close to the diameter of the reel seat for my desired seamless feel, I've often resorted to extremely skinny grips, which is tolerable on tiny rods but not so great on longer/heavier ones.
My last requirement has more to do with my own methods than anything else... I glue rings on the blank and then shape my grips and seats completely by hand, meaning I hold the rod butt in one hand and hold a mill-bastard file or garnet paper in the other. No lathe, no drill-rig, no jig. My grip/seat designs must facilitate being shaped by hand, yet still be straight and symmetrical. Enter my latest design:
This grip measures .94 inch at its fattest (behind the front taper). The "seat" tapers to .91 inch, considerably fatter than all but saltwater/salmon type rods.
How do I mount the reel, you ask? It's magic—no, simply O-rings. It's important that they're the 1/8 inch thick ones to ensure the reel is held securely. The rings roll up onto the reel foot and do not try to roll off unintentionally. O-rings last a long time, but are cheaply replaced at any hardware or plumbing supply store. Carrying a few spares is easy. The other little trick that this design accomplishes is the option to move the reel practically anywhere on the grip/seat. Grips may be fatter or skinnier than this—all that's needed is larger or smaller O-rings. This design also works for UL spinning.