Feeding outside of the enclosure is a myth. Infact it actually stresses the snake out more to feed it outside its enclosure because of the access handling after eating. Also, the "associating the enclosure with food" idea makes no sense. Because you are "associating" taking the snake out of its cage with eating when you remove it from its enclosure to feed it.
My snakes will know within the first 10 seconds I stick my hand into the cage if there is food or not, they usually will smell my hand, and once I touch them they know im not food.