I looked into Haggerty and Grundy (they seem to be the most popular in my area). Haggerty was to restrictive on the miles per year you can accumulate, something like 2500 (I drive my Barracuda about 6-7k per year), Grundy had no mileage limits. They both required the car to be garaged and both would not allow under 25 year old drivers.
Grundy seemed like the best for me and their on line questionaire asked if I ever drove the car to work or used it for errands which I answered yes and they gave me a ~$250 price for an $15K agreed value. When I got the paperwork they wanted signed and notorized documents that stated I would not use the car as alternate transportation, drive it to work or use it for errands. That basically takes them off the table as a potential insurer since I do all those things with mine from time to time.