at least fire her up every week, and leave her to warm up thoroughly (10-15 mins at idle at least)
I have heard from different sources, this is exactly what you should NOT do!
Every cold start is causing wear because of enriched fuel mixtures, the forming of condensed water in the engine oil and engine parts/cats/exhaustparts that will not warm through thouroughly being ran at idle revs.
Poluting the sparkplugs, combustionchambers, cats and the engine oil, is the sad result of multiple cold starts.
These engines should be ran at firm speeds and for a longer period of time, not just running at idle for ten minutes.
In that way the oil will reach at least its 90 degrees minimal temperature, nescecairy for evapourating waterdamp and petrol residues in the oil.
After the winterstop it is best to let the engine run for a minute or so and then drive it relaxed to a normal engine and oil temperature.
In my opinion every unnescecairy cold start should be avoided.