Far Cry 5 > Prepper Stash Locations and Walkthroughs
Stash Mission Start:
There is in a box front of the house at Tanami Residence, the island south of Baron Lumber Mill.
Activate dredge controls:
Go down to the dredge and dive through the window. All the way along the corridor. There are some stairs up at the end where you can breathe again.
Climb up the ladder at the end of the room, then go to the left. There's the switch. Use it.
Now you can enter the bunker through the hole the dredge just made. Just dive. You can dive up for air into a little cave. Follow the path inside the cave to the next dive pool. Take a dive again. There is a little air pocket you can dive up to if you need to. On the other side is the bunker door. Interact to open and you're inside. - CAREFUL: There's a snake in the room with the 3 perk magazines. Also the key card to open the locked door.