Probably too late, but have you considered the Tuneko covers ?
Less drag = Less fuel | Aluminium wheel hubcaps | Eco Tuning --> Tuneko Ltd
The guy who invented / makes them is a member here under the same name. Spendy maybe though but good quality by all accounts.
He is also into the 100+ MPG club with his VW Lupo 3L-2L project. (2 litres per 100 km)
And yes winter has hit here in Scotland.