Prepper Stash: Shipwreck
Find this stash at the Tanami Residence, on a Silver Lake island in Faith's patch.
The note is on the usual long crates, by the front door of the cabin.
The first step to gaining access here is to activate the trawler motor. You can swim in through a hole on the port (south) side of the dredge, just below the waterline.
Swim through the tunnel. You don't need the swimming perk and you don't need to do it all in one breath- – there are air pockets along the ceiling.
You'll swim north to the corner, then east, then south to some stairs up.
From there, head west inside the boat to the blue ladder up.
Up top, take the stairs down west to the switch.
Throw the switch, then exit the boat and go where the prow meets the island. Dive in and follow your marker.
Swim west, then surface. Go through the tunnel to the north.
Dive in the water again, and follow this tunnel all the way to the bunker entrance.
Pull yourself inside to complete the mission.
Note that there is a live snake here for some reason.
Also be sure to grab the keycard on the table with all the other loot. It'll allow you to open the main door, saving you a swim, and giving you access to the safe in the antechamber.