The stash is located at the Doverspike Compound (Northwest of US Auto). First, head inside the house and look for the Doverspike Key found on top of a drawer in the bedroom with the dead body. Head outside and enter the shed. Open the bunker hatch and drop inside.
The stash is hidden behind an electronic locked metal door near the entrance. However, it needs power to be unlocked. Head deeper inside the bunker until you reach a small room at the end with the breaker. Pull the lever to restore power to the room and start walking back to the entrance. Things will blow up around you so be careful on your way back. The door will be unlocked already so simply head inside and loot the contents of the stash.