This stash is hidden in the Hope County Jail Bus. There will be peggies in the location so get rid of them first before finding the note inside the bus and reading it. Follow the mission marker which leads to the drainage pipe downstream.
Head inside and turn right. Kill the wolverine and follow the pipe to reach the stash behind a locked gate. Backtrack to the main pipe and exit to the other side where you’ll find a bear munching on a corpse. Retrieve the key from the corpse and backtrack to the stash to loot it.