The vet said that if he survives the night he has a good chance. I usually let temps drop overnight, but I've put a ceramic heat emitter over him, some ceramic tile under him, and hoping for the best. The vet would like me to keep a high spot of 110F at all times, which might need some rigging, I can manage that fine in the day with a 100W bulb, but overnight is more tricky. Worst case I have a heat pad for my back that I can put in there with him, though I'd rather not as I'm sure it's a fire hazard to leave it on all night unsupervised. Got him up to about 90F with the heat emitter so far, think the next thing is to raise him up so he's closer to it, maybe. Difficult to do when he's needing to stay fairly immobile but is also keen to move about and self-regulate!