Accept the quest "Rocko's Modern Strife" and go to Thousand Cuts to start "Defend Slab Tower". You should notice that no foes will spawn in the area as long as you don't progress through the quest. Since normal foes will no longer spawn, you are free to circle the area and loot every chest without being hindered by enemies. However, foes such as one-armed bandits and loot midgets will still spawn. If you save and exit after clearing all the chests, you can just accept "Defend Slab Tower" once again and clear them out as many times as you like with the same conditions as long as you don't complete the quest.