Well the easiest way to get the most chances at getting chests are in the cosmodrome, skywatch and if the chest spawns close to the door you exit when there are a bunch of fallen/hive are fighting just take a sparrow and go at least halfway and then come back out to grab the chest again Personally my high score of chest I got I one run is 5 times, how many can you get? I have also got all my max keys and still currently hold 3 right now.