courgettes

as this "summer" has been a wash out i lost all my courgette plants from 2 packets of seed apart from one beautie who is fruiting well i am covering it with lots of fleece to keep it warm and avoid any frost which we may start to get from now on, i was wondering is it only frost that kills them or just cold weather, how long do you think it will survive and keep fruiting for covered up like this, on sunny days i will uncover it.
i am in surrey.

I will be only to glad to see the frosts kill them off    But to answer yep it generally is the frost that will kill them off.