ide not sleep in it, keep an eye on it, if needs be link a camera up to your computer and have it sneakily (so that noone can think oh theres a camera im gonna nick it) in the window pointing at the car just incase anything happens.
insurance is for that kinda thing, i know its bad and obviously you dont want the car torching but sitting in it is just gonna give you a crap nights sleep a cold and possibly more agro.
also the fact if you sleep in it tonight whats to stop them torching it tomorow or are you just gonna sleep in it forever