You don't say where you live butt, If I had an off street place to store my car I'd park the car and call my agent.  I'd tell my agent that I am not driving the car and take off the insurance needed legally to drive and put on the keep it in the garage insurance, some sort of comp with theft and fire. 

I do not have vintage plates, but in NY to cancel your car insurance you must turn in your plates.  The DMV provides you w/paperwork to give to your insurer.  I would beleive this is true for vintage plates also.  As suggested in another post, you should check w/you house insurer as the car may be covered for damage by house insurance if damaged while parked in your garage.
Another note, some municipalities do not allow cars to sit on your property w/o plates.  Of course, it is a different stroy if it is in a garage and no one can see it

FYI - the surrending of plates In NY in order to cancel insurance happened years ago.  In NY (going way back to the 50's I believe) you had to show 'proof of insurance' in order to get license plates.  People would make the initial insurance payment to obtain the proof of insurance, then cancel the insurance.  If this individual had an accident, well, you can figure out the problems this created.  Note that this was also before "no fault" insurance, so it was all on you to go after the other person for any compensation.