You would like to think an insurance company out there recognized what you were doing and say 6 months full insurance on each car on the road and 6 months theft only for the 6 months off the road. Dates specified. Link that with 6 months tax for each car (sorn when off the road) and it should mean the overall running costs for both cars over a year would be little more, maybe less, than what you currently pay.
But I guess that is far too complicated for the Insurance companies computer systems to deal with
Shedding insurance I like it. I'm only £800 for both cars and all mods declared anyway so can't really grumble too much.