So, got a few hundred km on it now. initailly, kept front cogs pretty clean, but was obvious some snow was getting on there, so cut up a foam disposable plate and slid it in behind the front mount, finally just got round to taping it up with black electrical tape so it doesn't look so obvious. Keeps the dirt off very well, I now need some lube on there, but haven't picked up any visible dirt at all. Next step is to manufacture a shield for the rear wheel to keep the water from washing off the lube.