Not that I've used it in a motorcycle application, but something I use a lot on bicycles is rubber mastic tape aka self-amalgamating tape aka self-fusing tape, made for electrical wrapping.
Stretchy rubber-as you wrap it, once stretched, it sticks to itself and forms a solid mass. Useful for a LOT of things. Was thinking that wrapped around frame rails, might do what you need it to do, and easily tailored for size/thickness.