You could place a couple of low wattage garage tube heaters under the exhausts when you leave the bike in the garage, that would evaporate the internal moisture out quickly, but I think the best option is just to forget about it, they’ll probably last 15 years, you’ll be 85 with probably more to worry about than rusty exhausts 🙂
That's a sobering thought 
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I like the suggestion of the tube heaters, i'll look into it but i will still try the Waxoyl route, the area that rots is the silencer, do they get hot enough to burn away the Waxoyl or just melt it into a liquid state which is ok.
They do get very hot, as does the gas travelling through them, it would almost certainly burn off the internal baffles, and probably run out of the drain holes causing a mess, , if you’re set on using it I’d try it in one silencer first, I think a low constant heat from a couple of tube heaters is your best bet , it would keep the rear of the bike bone dry as well 👍
