Hmmm... maybe for the hot water bottle, you could cut a hot water bottle shape out of felt or a heavy cloth... instead of water, stuff it with rice and sew closed. Then you can heat it in the microwave and pop it into his cage with him. It won't be an actual water bottle, but it will look like one, and probably retain heat better than an actual water bottle that size would.
that's an amazing idea!!! i have something just like that for myself when i have sore muscles...i could totally make one for the little guy...i just hope he wouldnt try to eat it!