I guess it's getting the worst of the weather and road conditions down there. You may find that a surprising amount will polish out with something like Autosol, then you could give it a coat of ACF50 (you can rub it on with a rag).
My stock silencer has been resting, uncovered, on a rafter right under the garage roof since I fitted the Goldie. It's still in good shape. The Goldie had a few very small rust spots, mostly top & side, which were easily polished out with Autosol. These from condensation in the garage. The underside is ok.
Spring has arrived in Devon and the bike is now out of its bag and on the road again. Three glorious 100 mile rides already. Ran a bit rough for the first couple of miles, but back to its former glory very quickly. It keeps sneaking up to seventy when I think I'm doing sixty, and seems quite relaxed about it. But I'm starting to keep an eye on the speedo until I'm re-aclimatised - a lot of harum scarum curves round these parts......