The wheel well's on the outside of the pressure hull, while the cargo hold's on the inside, so is pressurised. Or at least so I gather. It may not be heated ver

The wheel well's on the outside of the pressure hull, while the cargo hold's on the inside, so is pressurised. Or at least so I gather. It may not be heated very well, mind. Some random searching on the internet shows that the temperature of a cargo hold is about 10°C, and on at least one model of plane is (partially) heated by waste air from the cabins. Allegedly there's a flight deck switch which redirects the waste air overboard, which causes the temperature in the hold to plummet. This is known as the 'puppy snuffer' switch...