It is for that reason that I usually have only one key, which is in the ignition, plus a soft fabric or rubber fob, so no scratching. Two of my bikes have a separate ignition and fuel tank key (old bikes, replaced caps) and what I do there is cut a length of rubber fuel hose and put that over the sharp part of the fuel cap key so that when the ignition key is in, the fuel cap key can't scratch anything.
If you go with that strategy, there is no need for any protection whatsoever!
If you go with that strategy, there is no need for any protection whatsoever!