The car door doesn't get used that much so it is well locked most off the time. I used to keep a race car in there along with 10k worth of kit/tools so i reinforced the door with angle iron and put extra lockable bolts in place. The only other way in is from inside the house, the front door is being replaced in the next week or so with a upvc one which are very secure and you would have to get past two doors with 5 lever mortice locks at the back.