What would be the best way to keep a padlock secure if it is in a location where it is exposed to the elements such as rain, snow, and intense heat and cold?
There are several steps you can take to secure a padlock from degrading to the elements.  

First, you can choose a device designed to resistant damage due to moisture and extreme temperatures.

Second, sealing the padlock with grease such as Vasoline or other thick oil-based lubricants will prevent moisture from damaging the inner components.

Finally, periodic inspections should be performed to ensure the padlock is properly functioning, requires additional maintenance, or replacement if neccessary.