The height of the docks you dock at and the freeboard of the boats you raft with may vary, but the shape of YOUR boat's hull doesn't, and that is what you are protecting, so I have never understood the need for adjustability. What we did was hang out fenders from stainless snap hooks or carabiners, with a large enough mouth to fit around our stanchion bases. set the fender height, knot it, and it's done forever. Hanging fenders is as simple as snapping the shackle around the stanchion, and no pressure on the lifelines.
To solve the rubrail chafe problem, wrap the lines in leather chafe guards.
I took this idea one step further into the cheap zone. I bought those cheapo large aluminum carabiners 3 for a buck from the Dollar store and put two on each fender. One at the end of the fender line to clip onto the stantion base for fenders down and another carabiner right at the fender line knot to raise the fenders up and clip them high up on the life lines when sailing. When time comes to dock I just unclip from the life line and the fenders fall to the pre-determined hieght for the dock.