Altough you might only need insurance to drive it to the garage where its going to be stored have you thought about the worse case senario ie what if it gets nicked or the garage burns down ect hopefully it wont but for the sake of the cost of the insurance i would keep it insured all the time as its a big loss if the worse should happen. Im in the middle of doing the underside of my escos and it will be off the road for a year but it will still be insured the same regardless. As the car is worth more than £5000 its most likely that you will only be able to get fully comp insurance anyway.