Regardless of how hot or cold it is in the undercarriage bay - surely what kills stowaways is the lack of oxygen? I am not aware that the u/c bay is pressurised on most types and at 35,000 ft you will die of hypoxia within minutes. THEN if the temperature is -40 your body fluids will start to freeze.
To survive this type of environment you would need pressurised breathing apparatus and sufficient breathing air or oxygen for several hours above 30,000 ft+, and you would probably need your thermal undies on.
Anybody else know different?