I'm also seeing some posts about heat moldable plastic:
Heat moldable plastic? - Honda Motorcycles - FireBlades.org
I'll add that and "Form-in-place seal" (FIP Seal / Sealing
Compound MIL-S-8802) to the list above.
Another alternative I'm considering is pipe insulation foam (black foam with a slit) with paint or fiberglass over it to make it resistant to washing and road debris.