Multi-car insurance

[PhilboSE]

Any tips for a good multi-car insurance policy? I was hoping for something that recognised that I would be unlikely to drive more than one car at once. The easy-to-find websites (e.g. naval equivalent of a General) seem to quote on the basis of a normal policy for each car, with a pretty modest discount on the sum of the whole.

It's for 4 maybe 5 cars (two utilitarian and the others high performance). Don't need commercial use for any other than commuting. Trackday cover not required but wouldn't go amiss.