Far Cry 5 > Prepper Stash Locations and Walkthroughs
How to get the hint:
If you go south of Dutch's Bunker, you'll get to Johnson Lookout Tower. Save the civilian there and he will give you the stash hint as a reward.
At the stash location, read the note that the bunker is under water and it needs to be pumped out. For this, you need power from the boat house. Go to the next location, the boat house. Access the boat house through the water, get inside and switch on the power.
Marked Stash location
Marked Stash Location Note
Boat House Way in
Boat House Power Switch
To get out, you can also unlock the door. The keys are next to the door. Go back to where the bunker is, where the note was. There you can turn the big yellow wheel to pump the water out.
Go inside. The way is blocked straight ahead. Hit it with the melee weapon to get inside and finish the prepper mission.