So i was thinking: why do wastelanders think the best place to hide their blueprints and other junk is a brandnew footlocker near a wall?
There are less suspicious options for hiding stuff in city ruins. Or even in caves or woods, if he has a shovel.
Like a old NukaCola vending machine, newspaper box or a trunk of a car wreck, secured by a lock and explosive surprise.
If there is no treasure, a minor amount of junk, metal and electronic parts could be found in those containers.
This way, the treasure hunter will remain longer in encounter, though, but as he wants to find something he has to risk to encounter PKs or predators stumbling on him.